Deuteronomy 6:13

him shalt thou fear … serve … swear by his name Intended to cover the whole sphere of religion: the spiritual temper (on the frequent enforcement of the fear of God and its meaning see on Deuteronomy 4:10); acts of worship (the Hebrew term, though technically used of these, may cover other duties as well, see Driver, i. l.and cp. on Deuteronomy 10:12); and loyalty to God in all one's intercourse by word and deed with one's fellows. The reason for this last, which to our ears sounds strange in so brief a summary of religious duty, is clear. All the details of life are more explicitly connected with religion by primitive man than by ourselves. He naively and constantly appeals to his god for the truth of his statements and the honesty of his business transactions. So was it in the Israel of the deuteronomists" time, Jeremiah 5:2. Thus a man's oaths were in his everyday life the profession of his faith. If he swore by Baal, Baal was his god. Hence the need of the command to Israel here and in Jeremiah 4:2; Jeremiah 12:16. It is the duty of carrying out one's religion into the momentary details of life. Hence, too, the definition of Jehovah's true worshipper as he that sweareth by Jehovah, Psalms 63:11. But hence also the need for the presence among the Ten Commandments of one not to take Jehovah's name in vain. For the practice, however sincere in its origins, was terribly open to abuse, and was (and is) abused among Semitic nations beyond all others. Of the modern Arabs Doughty says, -they all day take God's name in vain (as it was perhaps in ancient Israel), confirming every light and laughing word with cheerful billahs," and -they will confirm any word with an oath" (Ar. Des.i. 265, 269). So Christ commanded, swear not at all.