Here a new section of the discourse begins, and is carried on to the end of the chapter. From the ideal picture of the life of the society which He came to found, our Lord passes to a protest against the current teaching of the scribes, sometimes adhering to the letter and neglecting the spirit, sometimes overriding even the letter by unauthorised traditions — lowering the standard of righteousness to the level of men’s practices, instead of raising their practices to the standard which God had fixed.
Think not that I am come. — The words imply that men had begun so to think. The Teacher who came preaching repentance, but also promising forgiveness, was supposed to be what in later times has been called Antinomian, attacking the authority of the two great channels through which the will of God had been revealed. “The Law and the prophets” were popularly equivalent to the whole of the Old Testament, though a strict classification required the addition of the Hagiographa, or “holy writings,” i.e., the poetical and miscellaneous books.
I am not come. — Better, I came not. The words might be naturally used by any teacher conscious of a mission, but they gain a new meaning when we remember that He who so spake was emphatically “He that should come;” that “He came into the world” not in the same sense as other men, but in a manner absolutely His own.
Not... to destroy, but to fulfil. — Explained by the immediate context, the words would seem to point chiefly to our Lord’s work as a teacher. He came to fill up what was lacking, to develop hints and germs of truth, to turn rules into principles. Interpreted on a wider scale, He came to “fulfil the Law and prophets,” as He came “to fulfil all righteousness” (3:15) by a perfect obedience to its precepts, to fulfil whatever in it was typical of Himself and His work by presenting the realities. The further thought that He came to fulfil what are called the Messianic prophecies hardly comes within the range of the words. No one could dream for a moment that the Christ could do anything else, and throughout the whole discourse there is no reference to those predictions. The prophets are named, partly in conformity with usage, partly in their character as ethical teachers, expounding and spiritualising the Law, and preparing the way for a further and fuller development.
It may be noted as a singular instance of the boldness of some of the early heretics, that Marcion, who rejected the Old Testament altogether, maintained that these words had been altered by the Judaisers of the apostolic age, and that the true reading was, “Think ye that I came to fulfil the Law or the prophets? I came not to fulfil, but to destroy.”