5:12 above all. This emphatic exhortation signals a weighty priority for godliness. To exalt refraining from false oaths and vows to a high level of priority may seem strange to some, but is consistent with the biblical concern for covenant-keeping and the sanctity of the faith.
do not swear. This is not a prohibition against cursing or the use of vulgarity. It concerns taking oaths by appealing to objects as witnesses (which in biblical terms is a form of idolatry). Only God has the power to be an omnipresent, omniscient witness to oaths and vows. Just and godly vows are not prohibited because they form a vital part of all covenants.
“yes” be yes. The Christian is expected to be a person whose word can be trusted. James’s teaching here echoes that of Jesus in the Sermon on the Mount (Matt. 5:34–37).