Rightly, therefore, the Scripture, in its desire to make us such dialecticians, exhorts us: "Be ye skilful money-changers" rejecting some things, but retaining what is good. For this true dialectic is the science which analyses the objects of thought, and shows abstractly and by itself the individual substratum of existences, or the power of dividing things into genera, which descends to their most special properties, and presents each individual object to be contemplated simply such as it is. [Strom 1.28]
"Lo, I make new things," saith the Word, "which eye hath not seen, nor ear heard, nor hath it entered into the heart of man." With a new eye, a new ear, a new heart, whatever can be seen and heard is to be apprehended, by the faith and understanding of the disciples of the Lord, who speak, hear, and act spiritually. For there is genuine coin, and other that is spurious; which no less deceives unprofessionals, that it does not the money-changers; who know through having learned how to separate and distinguish what has a false stamp from what is genuine. So the money-changer only says to the unprofessional man that the coin is counterfeit. But the reason why, only the banker's apprentice, and he that is trained to this department, learns. [Strom 2.4]
For truth is immoveable; but false opinion dissolves. We choose, for instance, one purple by comparison with another purple. So that, if one confesses that he has not a heart that has been made right, he has not the table of the money-changers or the test of words. And how can he be any longer a money-changer, who is not able to prove and distinguish spurious coin, even offhand? [Strom 6.10]
Further, it is said that it is on account of "those that are approved that heresies exist." [The apostle] calls "approved," either those who in reaching faith apply to the teaching of the Lord with some discrimination (as those are called skilful money-changers, who distinguish the spurious coin from the genuine by the false stamp), or those who have already become approved both in life and knowledge. [Strom 7.15]
Origen certainly knew the saying and implies - once again that the apostle was citing it while writing his letter to the Theasalonians:
The Apostle also speaks as if to "approved moneychangers." He says, "Testing all things, hold on to what is good."107 For it is only our Lord Jesus Christ who can teach you such a skill, through which you may know how to discern what is the money which bears the image of the true king, but also which is adulterous and, as the popular saying goes, is made outside the mint, which indeed bears the name of the king but does not have the genuine royal image. there are many who have the name of Christ but do not have the truth of Christ. And for this reason, the Apostle says, "for there must be heresies so that the genuine ones among you can become manifest." [Origen Homily on Leviticus 3]
Thus, when they have become approved money changers,8 they may carefully notice when I am a false teacher, when I truly speak things that are of piety and truth [Homily on Ezekiel 2]
The saying also appears as a 'gospel saying' in the Egyptian Pistis of Sophia:
When then Jesus had said this, Mary answered and said: "My Lord, if men go to seek and they come upon the doctrines of error, I whence then are they to know whether they belong to thee or not?" The Saviour answered and said unto Mary: "I have said unto you aforetime: 'Be ye as skilful money-changers. Take the good, throw the bad away.' The criterion of orthodoxy."Now, therefore, say unto all men who would seek the godhead: 'If north wind cometh, then ye know that there will be cold; if south wind cometh, then ye know that there will be burning and fervent heat.' Now, therefore, say unto them: 'If ye have known the face of the heaven and of the earth from the winds, then know ye exactly, if then any come now unto you and proclaim unto you a godhead, whether their words have harmonized and fitted with all your words which I have spoken unto you through two up to three witnesses, and whether they have harmonized in the setting of the air and of the heavens and of the circuits and of the stars and of the light-givers and of the whole earth and all on it and of all waters and all in them.' [Pistis Sophia 3.138]
Yet the saying ultimately seems to come from the writings of Philo strangely enough. We read in De Specialibus legibus iv.77 the same sense though with a slightly different word:
And let the man who undertakes the duty of a judge, like a skillful money-changer (Gk. arguramoibos agalhos], divide and distinguish between the natures of things, in order that confusion may not be caused by the mixing together of what is good and what is spurious."
Because of this parallel, Wright believes that the saying is derivative. Yet I would like to go one step further and argue that it demonstrates quite clearly that Clement and Dionysius were quite aware of an 'apostolic' but mystic Alexandrian gospel.