John Lightfoot on Matthew 5:17

[Think not that I am come to destroy the law, &c.] I. It was the opinion of the nation concerning the Messias, that he would bring in a new law, but not at all to the prejudice or damage of Moses and the prophets: but that he would advance the Mosaic law to the very highest pitch, and would fulfil those things that were foretold by the prophets, and that according to the letter, even to the greatest pomp.

II. The scribes and Pharisees, therefore, snatch an occasion of cavilling against Christ; and readily objected that he was not the true Messias, because he abolished the doctrines of the traditions which they obtruded upon the people for Moses and the prophets.

III. He meets with this prejudice here and so onwards by many arguments, as namely, 1. That he abolished not the law when he abolished traditions; for therefore he came that he might fulfil the law. 2. That he asserts, that "not one iota shall perish from the law." 3. That he brought in an observation of the law much more pure and excellent than the Pharisaical observation of it was: which he confirms even to the end of the chapter, explaining the law according to its genuine and spiritual sense.