Heidelberg Catechism LD #37

Lord's Day 37

101. But may we swear reverently by the name of God?

Yes, when the magistrate requires it, or when it may be needful otherwise, to maintain and promote fidelity and truth to the glory of God and our neighbor's good; for such an oath is grounded in God's Word,1 and therefore was rightly used by the saints in the Old and New Testaments.2

[1] Deut. 10:20; Isa. 48:1; Heb. 6:16. [2] Gen. 21:24; 31:53–54; Josh. 9:15, 19; 1 Sam. 24:22; 1 Kgs. 1:29; Rom. 1:9.

102. May we swear by “the saints” or by any other creatures?

No, for a lawful oath is a calling upon God, that He, as the only searcher of hearts, may bear witness to the truth, and punish me if I swear falsely;1 which honor is due to no creature.2

[1] 2 Cor. 1:23. [2] Matt. 5:34–36; *Jer. 5:7; *Isa. 65:16.