Matthew 5:19
Whoever sets aside one commandment of the law is set aside by God as a God-fighter and as one who legislates against God. And now from the gospel law he receives the punishment that the old law had not defined. So Christ says consistently that he did not come to destroy the law but to fulfill it (Matthew 5:17–19).
What was lacking there, he filled up here. The law said, “You shall rise before a gray head,” (Leviticus 19:32) and, “If you see your enemy’s beast fallen under its load, raise it with him.” (Exodus 23:5) If someone transgressed these, the law had defined no punishment. Filling that up, Christ says such a person will be set at nought in the kingdom of God. That is what he calls the least commandment: one on which no penalty was brought for transgression.
Greek
Ὁ ἀθετῶν μίαν τῶν τοῦ νόμου ἐντολῶν ἀθετεῖται παρὰ τοῦ θεοῦ ὡς θεομάχος καὶ ἀντινομοθετῶν τῷ θεῷ. καὶ νῦν ἐκ τοῦ εὐαγγελικοῦ νόμου δέχεται τὴν τιμωρίαν, ἣν νόμος πάλαι οὐκ ἦν ὁρίσας. διὸ καὶ ἀκολούθως λέγει ὁ Χριστός, "ὅτι οὐκ ἦλθον καταλῦσαι τὸν νόμον, ἀλλὰ πληρῶσαι". ὃ γὰρ ἐκεῖ ἔλειπε, ὧδε ἀνεπλήρωσεν, οἷον ἐν τῷ νόμῳ ἐλέ χθη· "ἀπὸ προσώπου πολιοῦ ἐξαναστήσῃ" καὶ "ἐὰν ἴδῃς τὸ ὑποζύγιον τοῦ ἐχθροῦ σου ὑποπεπτωκὸς ὑπὸ τὸν γόμον, συνέγειρον αὐτὸ μετ' αὐτοῦ". ταῦτα εἰ παρέβη τις, οὐκ ἦν τιμωρία ὁρισθεῖσα ὑπὸ τοῦ νόμου. ἣν ἀποπληρῶν ὁ Χριστός φησιν, ὅτι ἐν τῇ βασιλείᾳ τοῦ θεοῦ ὁ τοιοῦτος ἐξουθενηθήσεται. ταύτην οὖν καλεῖ ἐλαχίστην ἐντολήν, ἐφ' ἣν οὐκ ἦν ἐκ παραβάσεως ἐπαγομένη κόλασις.