I will grant that Christ said that he came not to destroy the law and the prophets, but to fulfill them. But why did Jesus say this? Was it to pacify the Jews, who were enraged at seeing their sacred institutions trampled upon by Christ, and regarded him as a wild blasphemer, not to be listened to, much less to be followed? Or was it for our instruction as Gentile believers, that we might learn meekly and patiently to bear the yoke of commandment laid on our necks by the law and the prophets of the Jews? You yourself can hardly suppose that Christ's words were intended to bring us under the authority of the law and the prophets of the Hebrews. So that the other explanation which I have given of the words must be the true one ... As "the law and the prophets" may have three different meanings, it is uncertain in what sense the words are used by Jesus, though we may form a conjecture from what follows. For if Jesus had gone on to speak of circumcision, and Sabbaths, and sacrifices, and the observances of the Hebrews, and had added something as a fulfillment, there could have been no doubt that it was the law and the prophets of the Jews of which He said that He came not to destroy, but to fulfill them. But Christ, without any allusion to these, speaks only of commandments which date from the earliest times: "You shall not kill; You shall not commit adultery; You shall not bear false witness." These, it can be proved, were of old promulgated in the world by Enoch and Seth, and the other righteous men, to whom the precepts were delivered by angels of lofty rank, in order to tame the savage nature of men. From this it appears that Jesus spoke of the law and the prophets of truth. And so we find him giving a fulfillment of those precepts already quoted. "You have heard," He says, "that it was said by them of old time, You shall not kill; but I say unto you, Be not even angry." This is the fulfillment. Again: "You have heard that it was said, You shall not commit adultery; but I say unto you, Do not lust even." This is the fulfillment. Again: "It has been said, You shall not bear false witness; but I say unto you, Swear not." This too is the fulfillment. He thus both confirms the old precepts and supplies their defects. Where He seems to speak of some Jewish precepts, instead of fulfilling them, He substitutes for them precepts of an opposite tendency. He proceeds thus: "You have heard that it has been said, An eye for an eye, and a tooth for a tooth; but I say unto you, Whosoever shall smite you on your right cheek, turn to him the other also." This is not fulfillment, but destruction. Again: "It has been said, You shall love your friend, and hate your enemy; but I say unto you, Love your enemies, and pray for your persecutors." This too is destruction. Again: "It has been said, Whosoever shall put away his wife, let him give her a writing of divorcement; but I say unto you, That whosoever shall put away his wife, saving for the cause of fornication, causes her to commit adultery, and is himself an adulterer if he afterwards marries another woman." Matthew 5:21-44 These precepts are evidently destroyed because they are the precepts of Moses; while the others are fulfilled because they are the precepts of the righteous men of antiquity. If you agree to this explanation, we may allow that Jesus said that he came not to destroy the law, but to fulfill it. If you disapprove of this explanation, give one of your own. Only beware of making Jesus a liar, and of making yourself a Jew, by binding yourself to fulfill the law because Christ did not destroy it
One could make a very persuasive case that these arguments were known to the Marcionites as well - albeit in some modified form - even though all the material is now found only in the Gospel of Matthew. As noted earlier, the gospel material appears 'antithetical' so it may well have helped shape Marcion's 'antitheses.'
The parallels between Augustine and the Diatessaron are well known. They were first detected by Louis Leloir, and others have been adduced by Gilles Quispel (VC 47 (1993), 374-378), and most recently by Tjitze Baarda. In another section of Contra Faustum (26.2) we find reference to the 'flying Jesus' tradition which again dates back to Marcion. Augustine quotes the Manichaean Faustus in order to refute him and in so doing reproduces the "throwing" of Jesus from the hill. Augustine does not comment on the varia lectio. Baarda notes "the agreement between Faustus and the Syriac texts suggests that the Manichaean was acquainted with the Diatessaron or at least with traditions that took their origin in this harmony. Remarkably enough, Augustin [sic] in his refutation does not mention the fact that Faustus used an argument for which [there] was no support in the canonical gospels. We cannot, therefore, exclude the possibility that Augustin knew this very tradition from his Manichaean past." [p. 78].
Yet as we return to chapter 19 we see Augustine begin to tackle the citation of the Diatessaron. While Augustine's response begins in section seven of the chapter, we read the following in section nineteen:
Faustus is wrong in supposing that the Lord Jesus fulfilled some precepts of righteous men who lived before the law of Moses, such as, "You shall not kill," which Christ did not oppose, but rather confirmed by His prohibition of anger and abuse; and that He destroyed some things apparently peculiar to the Hebrew law, such as, "An eye for an eye, and a tooth for a tooth," which Christ seems rather to abolish than to confirm, when He says, "But I say unto you, that you resist not evil; but if any one smite you on your right cheek, turn to him the other also," Matthew 5:38-39 and so on. But we say that even these things which Faustus thinks Christ destroyed by enjoining the opposite, were suitable to the times of the Old Testament, and were not destroyed, but fulfilled by Christ. [Contra Faustum 19.19]
Then in the very next section we see Augustine repeat the first line from Faustus's Diatessaron but follows that up with a verbatim citation from Matthew:
Will it be said that the law in these early times was incomplete as regards not committing adultery, till it was completed by the Lord, who added that no one should look on a woman to lust after her? This is what you imply in the way you quote the words, "You have heard that it has been said, You shall not commit adultery: but I say unto you, Do not lust even." "Here," you say, "is the fulfillment." But let us take the words as they stand in the Gospel, without any of your modifications, and see what character you give to those righteous men of antiquity. The words are: "You have heard that it has been said, you shall not commit adultery; but I say unto you, that whosoever looks on a woman to lust after her, has committed adultery with her already in his heart." [Matthew 5:27-28] In your opinion, then, Enoch and Seth, and the rest, committed adultery in their hearts; and either their heart was not the temple of God, or they committed adultery in the temple of God. But if you dare not say this, how can you say that Christ, when He came, fulfilled the law, which was already in the time of those men complete? [ibid 19:20]
It is interesting to note that no mention is made of the second line - 'thou shalt not be angry.' Yet it draws attention to an even deeper question - is the surviving text of Contra Faustum a reworking of a more original version of the debate - one in which Augustine at least feels comfortable using the Diatessaron?
The reason why we ask this is because the material which survives in the cantenae of the debate seems to preserve a more fluid situation - one more in keeping with an actual debate. For instance, it is very strange that at the beginning of Chapter Nineteen Faustus the Manichaean is portrayed as accepting the idea that Jesus once said 'I have not come to destroy the Law and the prophets but to fulfill them.' This even though Chapter Seventeen preserves Faustus making a very convincing argument against the authenticity of this statement. What is so interesting about Faustus's statement here is that it raises serious questions about the authenticity of the Catholic gospels. Indeed we can demonstrate quite easily that this material which has been moved to section seventeen actually formed part of Faustus's 'counter punch' against Augustine in the debate that followed his initial statement in Chapter Nineteen.
It is terribly significant for us to see that immediately following Faustus's lengthy discussion of Jesus's relation to the Law and the prophets - and his citation of the Diatessaron - the response of Augustine as preserved in Contra Faustum Chapter Nineteen Section Seven reads (in full):
Augustine replied: If you allow, in consideration of the authority of the Gospel, that Christ said that He came not to destroy the law and the prophets, but to fulfill them, you should show the same consideration to the authority of the apostle, when he says, "All these things were our examples;" and again of Christ, "He was not yea and nay, but in Him was yea; for all the promises of God are in Him yea;" that is, they are set forth and fulfilled in Him. In this way you will see in the clearest light both what law Christ fulfilled, and how He fulfilled it. It is a vain attempt that you make to escape by your three kinds of law and your three kinds of prophets. It is quite plain, and the New Testament leaves no doubt on the matter, what law and what prophets Christ came not to destroy, but to fulfill. The law given by Moses is that which by Jesus Christ became grace and truth. The law given by Moses is that of which Christ says, "He wrote of me." For undoubtedly this is the law which entered that the offense might abound; words which you often ignorantly quote as a reproach to the law. Read what is there said of this law: "The law is holy, and the commandment holy, and just, and good. Was then that which is good made death unto me? God forbid. But sin, that it might appear sin, wrought death in me by that which is good." The entrance of the law made the offense abound, not because the law required what was wrong, but because the proud and self-confident incurred additional guilt as transgressors after their acquaintance with the holy, and just, and good commandments of the law; so that, being thus humbled, they might learn that only by grace through faith could they be freed from subjection to the law as transgressors, and be reconciled to the law as righteous. So the same apostle says: "For before faith came, we were kept under the law, shut up unto the faith which was afterwards revealed. Therefore the law was our schoolmaster in Christ Jesus; but after faith came, we are no longer under a schoolmaster." That is, we are no longer subject to the penalty of the law, because we are set free by grace. Before we received in humility the grace of the Spirit, the letter was only death to us, for it required obedience which we could not render. Thus Paul also says: "The letter kills, but the spirit gives life." Again, he says: "For if a law had been given which could have given life, verily righteousness should have been by the law; but the Scripture has concluded all under sin, that the promise by faith of Jesus Christ might be given to them that believe." Galatians And once more: "What the law could not do, in that it was weak through the flesh, God sent His Son in the likeness of sinful flesh, that by sin He might condemn sin in the flesh, that the righteousness of the law might be fulfilled in us, who walk not after the flesh, but after the Spirit." Here we see Christ coming not to destroy the law, but to fulfill it. As the law brought the proud under the guilt of transgression, increasing their sin by commandments which they could not obey, so the righteousness of the same law is fulfilled by the grace of the Spirit in those who learn from Christ to be meek and lowly in heart; for Christ came not to destroy the law, but to fulfill it. Moreover, because even for those who are under grace it is difficult in this mortal life perfectly to keep what is written in the law, You shall not covet, Christ, by the sacrifice of His flesh, as our Priest obtains pardon for us. And in this also He fulfills the law; for what we fail in through weakness is supplied by His perfection, who is the Head, while we are His members. Thus John says: "My little children, these things write I unto you, that you sin not; and if any man sin, we have an Advocate with the Father, Jesus Christ the righteous: He is the propitiation for our sins." [ibid 19:7]
It is absolutely significant to keep your eye on the closing text which is emboldened here because the Catena Aurea preserves a variant of this text where Augustine is portrayed as mentioning not only the first part of the Diatessaronic reference of Faustus but also the part that is consistently omitted - not only in Augustine, but Clement of Alexandria and other Church Fathers - namely 'thou shalt not be angry.' What's more the Catena Aurea demonstrates that in the original text, the attack against the Gospel of Matthew which is now 'safely removed' to Chapter Seventeen, was part of Faustus's original assault on the Catholic tradition.
The Catena Aurea preserves Augustine's response as follows (emboldened black text for the parallel to the last citation, emboldened red for the mention of 'thou shalt not be angry'):
And lastly, because even for them who were under grace, it was hard in this mortal life to fulfil that of the Law, “Thou shalt not lust,” He being made a Priest by the sacrifice of His flesh, obtained for us this indulgence, even in this fulfilling the Law, that where through our infirmity we could not, we should be strengthened through His perfection, of whom as our head we all are members. For so I think must be taken these words, “to fulfil” the Law, by adding to it, that is, such things as either contribute to the explanation of the old glosses, or to enable to keep them. For the Lord has shewed us that even a wicked motion of the thoughts to the wrong of a brother is to be accounted a kind of murder. The Lord also teaches us, that it is better to keep near to the truth without swearing, than with a true oath to come near to blasphemy. But how, ye Manichaeans, do you not receive the Law and the Prophets, seeing Christ here says, that He is come not to subvert but to fulfil them?
To this the heretic Faustus replies, Whose testimony is there that Christ spoke this? That of Matthew. How was it then that John does not give this saying, who was with Him in the mount, but only Matthew, who did not follow Jesus till after He had come down from the mount?
To this Augustine replies, If none can speak truth concerning Christ, but who saw and heard Him, there is no one at this day who speaks truth concerning Him. Why then could not Matthew hear from John’s mouth the truth as Christ had spoken, as well as we who are born so long after can speak the truth out of John’s book? In the same manner also it is, that not Matthew’s Gospel, but also these of Luke and Mark are received by us, and on no inferior authority. And, that the Lord Himself might have told Matthew the things He had done before He called him. But speak out and say that you do not believe the Gospel, for they who believe nothing in the Gospel but what they wish to believe, believe themselves rather than the Gospel.
To this Faustus rejoins, We will prove that this was not written by Matthew, but by some other hand, unknown, in his name. For below he says, “Jesus saw a man sitting at the toll-office, Matthew by name.” [Matt 9:9] Who writing of himself say, ‘saw a man,’ and not rather, ‘saw me?’
Augustine; Matthew does no more than John does, when he says, “Peter turning round saw that other disciple whom Jesus loved;” as it is well known that this is the common manner of Scripture writers, when writing their own actions.
Faustus again, But what say you to this, that the very assurance that He was not come to destroy the Law and the Prophets, was the direct way to rouse their suspicions that He was? For He had yet done nothing that could lead the Jews to think that this was His object.
Augustine; This is a very weak objection, for we do not deny that to the Jews who had no understanding, Christ might have appeared as threatening the destruction of the Law and the Prophets.
Faustus; But what if the Law and the Prophets do not accept this fulfilment, according to that in Deuteronomy,
Augustine; Here Faustus does not understand what it is to fulfil the Law, when he supposes that it must be taken of adding words to it. The fulfilment of the Law is love, which the Lord hath given in sending His Holy Spirit. The Law is fulfilled either when the things there commanded are done, or when the things there prophesied come to pass.
Faustus; But in that we confess that Jesus was author of a New Testament, what else is it than to confess that He has done away with the Old?
Augustine; In the Old Testament were figure of things to come, which, when the things themselves were brought in by Christ, ought to have been taken away, that in that very taking away the Law and the Prophets might be fulfilled wherein it was written that God gave a New Testament.
Faustus; Therefore if Christ did say this thing, He either said it with some other meaning, or He spoke falsely, (which God forbid,) or we must take the other alternative, He did not speak it at all. But that Jesus spoke falsely none will aver, therefore He either spoke it with another meaning, or He spake it not at all. For myself I am rescued from the necessity of this alternative by the Manichaean belief, which from the first taught me not to believe all those things which are read in Jesus’ name as having been spoken by Him; for that there be many tares which to corrupt the good seed some nightly sower has scattered up and down through nearly the whole of Scripture.
Augustine; Manichaeus taught an impious error, that you should receive only so much of the Gospel as does not conflict with your heresy, and not receive whatever does conflict with it. We have learned of the Apostle that religious caution, “Whoever preaches unto you another Gospel than that we have preached, let him be accursed.” [Gal 1:8] The Lord also has explained what the tares signify, not things false mixed with the true Scriptures, as you interpret, but men who are children of the wicked one.
Faustus; Should a Jew then enquire of you why you do not keep the precepts of the Law and the Prophets which Christ here declares He came not to destroy but to fulfil, you will be driven either to accept an empty superstition, or to repudiate this chapter as false, or to deny that you are Christ’s disciple.
Augustine; The Catholics are not in any difficulty on account of this chapter as though they did not observe the Law and the Prophets; for they do cherish love to God and their neighbour, “on which hang all the Law and the Prophets.” And whatever in the Law and the Prophets was foreshewn, whether in things done, in the celebration of sacramental rites, or in forms of speech, all these they know to be fulfilled in Christ and the Church. Wherefore we neither submit to a false superstition, nor reject the chapter, nor deny ourselves to be Christ’s disciples. He then who says, that unless Christ had destroyed the Law and the Prophets, the Mosaic rites would have continued along with the Christian ordinances, may further affirm, that unless Christ had destroyed the Law and the Prophets, He would yet be only promised as to be born, to suffer, to rise again. But inasmuch as He did not destroy, but rather fulfil them, His birth, passion, and resurrection, are now no more promised as things future, which were signified by the Sacraments of the Law; but He is preached as already born, crucified, and risen, which are signified by the Sacraments now celebrated by Christians. It is clear then how great is the error of those who suppose, that when the signs or sacraments are changed, the things themselves are different, whereas the same things which the Prophetic ordinance had held forth as promises, the Evangelic ordinance points to as completed.
Faustus: Supposing these to be Christ’s genuine words, we should enquire what was His motive for speaking thus, whether to soften the blind hostility of the Jews, who when they saw their holy things trodden under foot by Him, would not have so much as given Him a hearing; or whether He really said them to instruct us, who of the Gentiles should believe, to submit to the yoke of the Law. If this last were not His design, then the first must have been; nor was there any deceit or fraud in such purpose. For of laws there be three sorts. The first that of the Hebrews, called the “law of sin and death,” [Rom 8:2] by Paul; the second that of the Gentiles, which he calls the law of nature, saying, “By nature the Gentiles do the deeds of the law;” [Rom 2:14] the third, the law of truth, which he means, “The law of the Spirit of life.” Also there are Prophets some of the Jews, such as are well known; others of the Gentiles as Paul speaks, “A prophet of their own hath said;” [Tit 1:12] and others of the truth of whom Jesus speaks, “I send unto you wise men and prophets.” [Matt 23:34] Now had Jesus in the following part of this Sermon brought forward any of the Hebrew observances to shew how he had fulfilled them, no one would have doubted that it was of the Jewish Law and Prophets that He was now speaking; but when He brings forward in this way only those more ancient precepts, “Thou shalt not kill, Thou shalt not commit adultery,” which were promulged of old to Enoch, Seth, and the other righteous men, who does not see that He is here speaking of the Law and Prophets of truth? Wherever He has occasion to speak of any thing merely Jewish, He plucks it up by the very roots, giving precepts directly the contrary; for example, in the case of that precept, “An eye for an eye, a tooth for a tooth.”
Augustine; Which was the Law and which the Prophets, that Christ came “not to subvert but to fulfil,” is manifest, to wit, the Law given by Moses. And the distinction which Faustus draw between the precepts of the righteous men before Moses, and the Mosaic Law, affirming that Christ fulfilled that one but annulled the other, is not so. We affirm that the Law of Moses was both well suited to its temporary purpose, and was not now subverted, but fulfilled by Christ, as will be seen in each particular. This was not understood by those who continued in such obstinate error, that they compelled the Gentiles to Judaize - those heretics, I mean, who were called Nazarenes.
It is incredibly to witness how this original material has been manipulated in the surviving Contra Faustum. If we work in reverse order - Augustine's statement about the Nazarenes has now been put into Faustus's mouth, and a whole silly argument about 'being Jewish' is developed which is so absurd it was impossible to associate with Faustus even without this information.
Yet far more serious is the fact that the long discussion of 'three types' of law which originally only formed an appendage to the main argument has - in Contra Faustum - been moved up into Faustus's main argument. This was done clearly to obscure the fact that the original discussion was not about "what Jesus meant by 'I have come to fulfill the Law and the prophets'" - another absurd manipulation of the text. A later editor came along and realized that Augustine did not come out looking that great in his original debate over the Diatessaronic juxtaposition between the commandments of Moses and the three 'lost commandments' of Jesus ('thou shalt not lust, thou shalt not be angry, thou shalt not swear') and so a new 'debate' was forged. We can be relatively certain that Augustine did indeed debate Faustus from the Diatessaron.