Luke 16:17

But lest they should suppose that in His words, the Law and the Prophets were until John, He preached the destruction of the Law or the Prophets, He obviates such a notion, adding, And it is easier for heaven and earth to pass, than one tittle of the law should fail. For it is written, the fashion of this world passeth away. (1 Cor. 7:31.) But of the Law, not even the very extreme point of one letter, that is, not even the least things are destitute of spiritual sacraments. And yet the Law and the Prophets were until John, because that could always be prophesied as about to come, which by the preaching of John it was clear had come. But that which He spoke beforehand concerning the perpetual inviolability of the Law, He confirms by one testimony taken therefrom for the sake of example, saying, Whosoever putteth away his wife, and marrieth another, committeth adultery: and whosoever marrieth her that is put away from her husband, committeth adultery; that from this one instance they should learn that He came not to destroy but to fulfil the commands of the Law.

Not that the Law failed, but that the preaching of the Gospel began; for that which is inferior seems to be completed when a better succeeds. For the Law delivered many things according to nature, as being more indulgent to our natural desires, that it might call us to the pursuit of righteousness. Christ breaks through nature as cutting off even our natural pleasures. But therefore we keep under nature, that it should not sink us down to earthly things, but raise us to heavenly.