But above all - as swearing is utterly alien to the Christian meek “endurance” just recommended.
swear not - through impatience, to which trials may tempt you (Jam 5:10, Jam 5:11). In contrast to this stands the proper use of the tongue, Jam 5:13. James here refers to Mat 5:34, etc.
let your yea be yea - Do not use oaths in your everyday conversation, but let a simple affirmative or denial be deemed enough to establish your word.
condemnation - literally, “judgment,” namely, of “the Judge” who “standeth before the doors” (Jam 5:9).