Because it is a great sin to swear upon every slight occasion, and it was very usual among the Jews, and it was the more difficult to bring them off from it who were so much accustomed to it; therefore the apostle commands them, that above all things they should not swear, i.e. should take special care they did not, and watch diligently against a sin so many were addicted to, and into which they might so easily fall. Swear not; all swearing is not forbidden, any more than Matthew 5:34; (for oaths are made use of by holy men both in the Old and New Testament, Genesis 21:23,24 Genesis 24:3 26:28 1 Kings 17:1,2 2 Corinthians 1:23 Galatians 1:20; and the use of an oath is permitted and approved of by God himself, Psalms 15:4 Hebrews 6:16); but such oaths as are false, rash, vain, without just cause, or customary and frequent in ordinary discourse, 1 Kings 19:2 Jeremiah 5:2 Matthew 5:37. Neither by heaven, neither by the earth; by which the Jews thought they might lawfully swear, as likewise by other creatures, so the name of God were not interposed; not considering that where it is not expressed yet it is implied, Matthew 23:20,21. Neither by any other oath; viz. of the like kind. But let your yea be yea; and your nay, nay: either:
1. Let your speech be yea, yea, and nay, nay; i.e. by plain affirmations and negations, without the addition of any oath for confirmation, Matthew 5:37: or: 2. Let your yea be yea, and your nay, nay, i.e. let your words be in truth and sincerity, your speech seconded by your actions; accustom yourselves to truth and plainness in speaking, and that will take away the occasion of swearing. See the like, 2 Corinthians 1:17-19. Lest ye fall into condemnation; viz. for taking the name of God in vain, Exodus 20:7, which is always done in an unwarrantable oath.