Above all things - swear not - What relation this exhortation can have to the subject in question, I confess I cannot see. It may not have been designed to stand in any connection, but to be a separate piece of advice, as in the several cases which immediately follow. That the Jews were notoriously guilty of common swearing is allowed on all hands; and that swearing by heaven, earth, Jerusalem, the temple, the altar, different parts of the body, was not considered by them as binding oaths, has been sufficiently proved. Rabbi Akiba taught that "a man might swear with his lips, and annul it in his heart; and then the oath was not binding." See the notes on Matthew 5:33, etc., where the subject is considered in great detail.
Let your yea be yea, etc. - Do not pretend to say yea with your lips, and annul it in your heart; let the yea or the nay which you express be bona fide such. Do not imagine that any mental reservation can cancel any such expressions of obligation in the sight of God.
Lest ye fall into condemnation - Ἱνα μη ὑπο κρισιν πεσητε· Lest ye fall under judgment. Several MSS. join ὑπο and κρισιν together, ὑποκρισιν, and prefix εις, into, which makes a widely different reading: Lest ye fall into hypocrisy. Now, as it is a fact, that the Jews did teach that there might be mental reservation, that would annul the oath, how solemnly soever it was taken; the object of St. James, if the last reading be genuine, and it is supported by a great number of excellent MSS., some versions, and some of the most eminent of the fathers, was to guard against that hypocritical method of taking an oath, which is subversive of all moral feeling, and must make conscience itself callous.
But above all things - That is be especially careful on this point; whatever else is done, let not this be. The manner in which James speaks of the practice referred to here, shows that he regarded it as a sin of a very heinous nature; one that was by all means to be avoided by those whom he addressed. The habit of swearing by various things was a very common one among the Jews, and it was important to guard those who from among them had been converted to Christianity on that subject.
Swear not - See this command illustrated in the notes at Matthew 5:33-34. Nearly the same things are mentioned here, as objects by which they were accustomed to swear, which are referred to by the Saviour.
But let our yea be yea - Let there be a simple affirmation, unaccompanied by any oath or appeal to God or to any of his works. A man who makes that his common method of speech is the man who will be believed. See the notes at Matthew 5:37.
Lest you fall into condemnation - That is, for profaning the name of God. “The Lord will not hold him guiltless that taketh his name in vain,” Exodus 20:7.