CCC 577

At the beginning of the Sermon on the Mount Jesus issued a solemn warning in which he presented God's law, given on Sinai during the first covenant, in light of the grace of the New Covenant: Do not think that I have come to abolish the law or the prophets: I have come not to abolish but to fulfil. For truly I tell you, until heaven and earth pass away, not one letter, not one stroke of a letter, will pass from the law, until all is accomplished. Therefore, whoever breaks one of the least of these commandments, and teaches others to do the same, will be called least in the kingdom of heaven; but whoever does them and teaches them will be called great in the kingdom of heaven.