I forgot to post the next series of question from the catechism on the third command:
Question #101: But may we swear an oath in God's name if we do it reverently?
Answer: Yes, when the government demands it, or when necessity requires it, in order to maintain and promote truth and trustworthiness for God's glory and our neighbor's good.
Such oaths are approved in God's Word and were rightly used by Old and New Testament believers (Deut. 6:13; 10:20; Jer. 4:1-2; Heb. 6:16; Gen. 21:24; Josh. 9:15; 1 Kings 1:29-30; Rom. 1:9; 2 Cor. 1:23).
Question #102: May we swear by saints or other creatures?
Answer: No. A legitimate oath means calling upon God as the one who knows my heart to witness to my truthfulness and to punish me if I swear falsely. No creature is worthy of such honor (Rom. 9:1; 2 Cor. 1:23; Matt. 5:34-37; 23:16-22; James 5:12).