Matthew 5:33

33.Thou shalt not perjure thyself This also is not a correction of the law, but a true interpretation of it. For God condemned in the law not only acts of perjury, but lightness in swearing, which lessens the reverence for his name. The man who perjures himself is not the only person who takes the name of God in vain, (Exodus 20:7.) He does so, who idly and contemptuously pronounces the name of God on trivial occasions, or in ordinary conversation. While the law condemns every kind of profanation of the name of God the Jews imagined, that the guilt of it lay entirely in acts of perjury. Christ reproves this gross error of supposing that they might, without danger, abuse the name of God, provided they did not swear falsely. We are, no doubt, strictly enjoined to perform to the Lord what we have sworn: for he who, after employing the name of God, cheats and deceives his neighbors, does an injury to God as well as to man. But it is improper to confine to a single part that which has a wider reference. Some consider the word perform as applying to vows, when any thing has been promised to God on account of religion. But this mode of expression applies very well to all promises and engagements, which have been sanctioned by the use of the name of God: for in such cases God is appealed to as guarantee between the parties, to secure their fidelity.