Heidelberg Catechism – Lord’s Day 37
Q. But may we not swear oaths by the name of God in a devout manner?
A. Yes, when the civil authorities require it of their subjects, or when it is otherwise needed to maintain and promote fidelity and truth, to the glory of God and the welfare of our neighbor. Such oath-taking is grounded in God’s Word and has therefore been rightly used by God’s people under the Old and New Covenants.
Q. May we also swear by the saints or other creatures?
A. No; for a lawful oath is a calling upon God, as the only searcher of hearts, to bear witness to the truth, and to punish me if I swear falsely. No creature deserves such honor.