James 5:12

From the need of patient endurance we are next warned of the danger of light or thoughtless asseverations in ordinary speech: a common habit among both Jews and Greeks, but wholly unworthy of Him Who is the truth, the great exemplar for all who confess Him Lord. “But before all things, my brethren, swear not, neither by heaven, nor by the earth, nor by any other oath; but let your yea be yea, and nay nay, lest ye fall under judgment” (ver. 12). As sinning with the tongue is throughout denounced, so here in particular the lack of reverence. For though the oaths is question refer to the creature rather than to God, though they may affect care for His name by substituting other forms for His; who entitles men to adopt anything of the sort in daily intercourse? He is the Judge, Who has assured us that of every idle word that men speak they shall give account in the day that comes; “for by thy words thou shalt be justified, and by thy words thou shalt be condemned.”
Indeed on the mount, in the great series of discourses of which the first Gospel gives the summary, the Lord had pronounced on the same wrong. “Again, ye have heard that it was said to those of old time, Thou shalt not perjure thyself, but shalt perform to Jehovah thy vows; but I say to thee, Swear not at all: neither by the heaven, for it is God's throne; nor by the earth, for it is the footstool of his feet; nor by Jerusalem, for it is the city of the great King. No more shalt thou swear by thy head; for thou canst not make one hair white or black. But let your word be yea, yea; nay, nay; for that which is more cometh of evil” (or, the evil one). The selfsame duty is enforced as in this Epistle.
It is a total mistake to conceive that by either a judicial oath is forbidden. The specimens given preclude such an inference. They are not such as the magistrate puts in a court or other occasion; they were, or might be, the common phrases of every day. The sense therefore is clearly given by the A.V. rendering of “your communication.” It was not an answer to the demand of one entitled to ask in God's name. This every one is bound to give. So our Lord was silent till the High Priest adjured, or put the oath, with that authority; as the O.T. claims it in Lev. 5:11And if a soul sin, and hear the voice of swearing, and is a witness, whether he hath seen or known of it; if he do not utter it, then he shall bear his iniquity. (Leviticus 5:1). Here it is only the case of man with man. Even without a magistrate, but on an adequately solemn occasion we have the apostle confirming what he taught the saints by an equivalent, as in Rom. 1:9; 9:19For God is my witness, whom I serve with my spirit in the gospel of his Son, that without ceasing I make mention of you always in my prayers; (Romans 1:9)
1I say the truth in Christ, I lie not, my conscience also bearing me witness in the Holy Ghost, (Romans 9:1)
, 2 Cor. 1:2323Moreover I call God for a record upon my soul, that to spare you I came not as yet unto Corinth. (2 Corinthians 1:23), Gal. 1:2020Now the things which I write unto you, behold, before God, I lie not. (Galatians 1:20), Phil. 1:88For God is my record, how greatly I long after you all in the bowels of Jesus Christ. (Philippians 1:8), 2 Thess. 3:55And the Lord direct your hearts into the love of God, and into the patient waiting for Christ. (2 Thessalonians 3:5); so he adjures his brethren in 1 Thess. 5:2727I charge you by the Lord that this epistle be read unto all the holy brethren. (1 Thessalonians 5:27).
It is quite enough that in our converse with brethren or other men our yea should be yea, and our nay nay. “That which is more cometh of evil.” The believer is as responsible to speak as to act in the presence of God. This is his habitual privilege, and safeguard. It may be forgotten by others, or by himself to his loss. The evil one is a liar and the father of it. No small opportunity would it be to him if the Christian were not always watchful to speak truly, and needed such expletives to gain credit for it.