V. Christ not destroyed, but fulfilled and elevated the Law
As therefore there is no believer, dearly-beloved, to whom the gifts of grace are denied, so there is no one who is not a debtor in the matter of Christian discipline; because, although the severity of the mystic Law is done away, yet the benefits of its voluntary observance have increased, as the evangelist John says, “Because the Law was given through Moses, but grace and truth came through Jesus Christ.” For all things that, according to the Law, went before, whether in the circumcision of the flesh, or in the multitude of victims, or in the keeping of the Sabbath, testified of Christ, and foretold the grace of Christ. And He is “the end of the Law,” not by annulling, but by fulfilling its meanings. For although He is at once the Author of the old and of the new, yet He changed the symbolic rites connected with the promises, because He accomplished the promises and put an end to the announcement by the coming of the Announced. But in the matter of moral precepts, no decrees of the earlier Testament are rejected, but many of them are amplified by the Gospel teaching: so that the things which give salvation are more perfect and clearer than those which promise a Saviour.
Source: Sermons (New Advent)