Q. 101
But may we swear an oath by the name of God in a godly manner?
A.
Yes, when the government demands it of its subjects, or when necessity requires it, in order to maintain and promote fidelity and truth, to God's glory and for our neighbour's good. Such oath-taking is grounded in God's Word and was therefore rightly used by saints in the Old and the New Testament.
Scripture Deuteronomy 6:13 · Deuteronomy 10:20 · Hebrews 6:16
Q. 102
May we also swear by saints or other creatures?
A.
No. A lawful oath is a calling upon God, as the only one who knows the heart, to bear witness to the truth, and to punish me if I swear falsely. No creature is worthy of such honour.
Scripture Matthew 5:34-37 · James 5:12