By them of old time (Matthew 5:21, note). Thou shalt not forswear thyself ( οὐκ ἐπιορκήσεις). These two words are the substance of Le Matthew 19:12, which itself (cf. Rashi, in loc.) includes a reference to the third commandment.
To them our Lord joins but shalt perform, etc., which is the substance of Deuteronomy 23:23 (cf. Numbers 30:2). (On our Lord's utterance representing the current form of teaching about oaths, cf. Deuteronomy 23:21, note.
) This current teaching was the logical deduction from the statements of the Law, and yet the Law had a higher aim.