Since Judaism attempts to sanctify the holy name of God by leaving it unpronounced and even avoids circumlocutions like “Adonai” outside of a liturgical context, people taking oaths and vows sought ways around swearing directly in God’s name. In Matthew 5:33, the Master quoted two passages of Torah (Leviticus 19:12; Numbers 30:3) that dishonest people apparently used in tandem to imply that only vows made in the name of the LORD were absolutely inviolable.
Again, you have heard that the ancients were told, “You shall not make false vows, but shall fulfill your vows to the LORD.” (Matthew 5:33)
According to some opinions of the time, a man is bound by an oath only when it contains the word “oath” in it or God’s name. An oath by any other holy object does not bind the man. The same issue was at work behind the Master’s rebuke in Matthew 23:16-22. In that passage, those who had sworn by the altar or by the Temple felt that, since they had avoided directly using God’s name, they were not bound to their vow.
Because people commonly used circumlocutions for God’s name such as vowing by heaven, vowing by earth or even vowing by Jerusalem, they felt less bound to their vows and oaths. Rabbi Yeshua warned His disciples that swearing by heaven or by earth is the same as swearing in the name of God because “Heaven is God’s throne and the earth is His footstool” (Isaiah 66:1). He warned them that swearing by Jerusalem is the same as swearing in God’s name because Jerusalem is “the city of the great King” (Psalm 48:3). According to some opinions, an oath taken on one’s own life could be retracted. Yeshua said, “Nor shall you make an oath by your head, for you cannot make one hair white or black” (Matthew 5:36).
James the brother of the Master recapitulates, “But above all, my brethren, do not swear, either by heaven or by earth or with any other oath; but your yes is to be yes, and your no, no, so that you may not fall under judgment” (James 5:12).
Obviously some vows (i.e., marriage, nazirism) are necessary, and the Master’s prohibition should not be regarded as a ban on contracts or promises. Instead, His disciples are to be a people of such immense integrity that our simple ‘yes’ is equivalent to an oath taken in the name of God. We are to be a people of such integrity, that no further verification is needed from us other than a ‘yes’ or a ‘no.’ The sages agree with the Master’s teaching. According to rabbinic standards of the Master’s day, an emphatic ‘yes’ or an emphatic ‘no’ should be regarded as binding as an oath.
Rabbi Eleazar said, “‘No’ is an oath and ‘Yes’ is an oath.” (b.Shevu’ot 36a)
Rabbi Huna said in the name of Rabbi Shmuel ben Yitzchak, “The ‘Yes’ of the righteous is a yes, and the ‘No’ of the righteous is no.” (Ruth Rabbah 7:6)