5:33 {8} Again, ye have heard that it hath been said by them of old time, Thou shalt not forswear thyself, but shalt perform unto the Lord thine oaths:
(8) The meaning of the third commandment against the perverse opinion and judgment of the scribes, who excused by oaths or indirect forms of swearing.
5:33 Thou shalt not forswear thyself. See Le 19:12 Nu 25:2. The Jews held that this only prohibited swearing falsely and by the name of God.
5:33 Our Lord here refers to the promise made to the pure in heart of seeing God in all things, and points out a false doctrine of the scribes, which arose from their not thus seeing God. What he forbids is, the swearing at all, by any creature, in our ordinary conversation: both of which the scribes and Pharisees taught to be perfectly innocent. Exod 20:7.
5:33-37 There is no reason to consider that solemn oaths in a court of justice, or on other proper occasions, are wrong, provided they are taken with due reverence. But all oaths taken without necessity, or in common conversation, must be sinful, as well as all those expressions which are appeals to God, though persons think thereby to evade the guilt of swearing. The worse men are, the less they are bound by oaths; the better they are, the less there is need for them. Our Lord does not enjoin the precise terms wherein we are to affirm or deny, but such a constant regard to truth as would render oaths unnecessary.
