Matthew 15:24, 26

Now, the Gentiles knew nothing either of Him, or of any of His promises. Therefore it was to Israel that he spake when He said, "I am not sent but to the lost sheep of the house of Israel." (Matthew 15:24) Not yet had He "cast to the dogs the children's bread" (Matthew 15:26) not yet did He charge them to "go into the way of the Gentiles." It is only at the last that He instructs them to "go and teach all nations, and baptize them," when they were so soon to receive "the Holy Ghost, the Comforter, who should guide them into all the truth." And this, too, makes towards the the same conclusion. If the apostles, who were ordained to be teachers to the Gentiles, were themselves to have the Comforter for their teacher, far more needless was it to say to us, "Seek, and ye shall find," to whom was to come, without research, our instruction by the apostles, and to the apostles themselves by the Holy Ghost. All the Lord's sayings, indeed, are set forth for all men; through the ears of the Jews have they passed on to us. Still most of them were addressed to Jewish persons; they therefore did not constitute instruction properly designed for ourselves, but rather an example. [Tertullian De praescriptionibus aduersus haereses omnes 8.13]

But since both the place and the work of illumination according to the prophecy are compatible with Christ, we begin to discern that He is the subject of the prophecy, which shows that at the very outset of His ministry, He came not to destroy the law and the prophets, but rather to fulfil them for Marcion has erased the passage as an interpolation. It will, however, be vain for him to deny that Christ uttered in word what He forthwith did partially indeed. For the prophecy about place He at once fulfilled. From heaven straight to the synagogue. As the adage runs: "The business on which we are come, do at once." Marcion must even expunge from the Gospel, "I am not sent but unto the lost sheep of the house of Israel;" and, "It is not meet to take the children's bread, and to cast it to dogs," ----in order, forsooth, that Christ may not appear to be an Israelite. But facts will satisfy me instead of words. Withdraw all the sayings of my Christ, His acts shall speak. Lo, He enters the synagogue; surely (this is going) to the lost sheep of the house of Israel. Behold, it is to Israelites first that He offers the "bread" of His doctrine; surely it is because they are "children" that He shows them this priority. Observe, He does not yet impart it to others; surely He passes them by as "dogs." For to whom else could He better have imparted it, than to such as were strangers to the Creator, if He especially belonged not to the Creator? And yet how could He have been admitted into the synagogue----one so abruptly appearing, so unknown; one, of whom no one had as yet been apprised of His tribe, His nation, His family, and lastly, His enrolment in the census of Augustus----that most faithful witness of the Lord's nativity, kept in the archives of Rome? They certainly would have remembered, if they did not know Him to be circumcised, that He must not be admitted into their most holy places. And even if He had the general right of entering the synagogue (like other Jews), yet the function of giving instruction was allowed only to a man who was extremely well known, and examined and tried, and for some time invested with the privilege after experience duly attested elsewhere. [Tertullian Adv Marc 4.7.5 KROYMANN Aem., CCL 1 (1954)(p.554, l.1) BP1]