"Swear not at all." --- Matthew 5:34.
Swear not by the creatures: that in effect is swearing by the their maker. Neither swear by the Maker, unless called to it by authority for the putting an end to strife: swear not falsely, that is, calling the God of truth to witness a lie: Swear not needlessly or rashly, as Saul did. 1 Samuel 14:39.
Such oaths or vows are ensnaring; better broken than kept; but best not made at all. Swear not idle, common oaths, such as O Christ! O God! faith and troth! by my soul, as I live! God bless me!. If we must give account of every idle word, much more for every idle oath, and most of all for horrible cursing and blasphemy that profane God's name, and is the very language of hell.
He that is guilty of perjury, not only is destroying his own soul, but is seeking to ruin his neighbour, by perverting justice and robbing the innocent of his right. Yes, sometimes God takes a false-swearer and self-curser at his word, and strikes him dead on the spot. Lord, help the guilty to repent of their sin, and help all to watch and pray against it.
From false and rash and idle oaths
Defend my tongue, O Lord;
Let salt of grace hang on my lips,
To season every word.