Heidelberg Catechism · 1563

Q102. May we also swear by saints or other creatures?

No. A lawful oath is a calling upon God, who alone knows the heart, to bear witness to the truth, and to punish me if I swear falsely. No creature is worthy of such honour.
Answer · Heidelberg Catechism

Scripture proofs

  1. [1]
    Romans 9:1

    I say the truth in Christ, I lie not, my conscience also bearing me witness in the Holy Ghost,

    2 Corinthians 1:23

    Moreover I call God for a record upon my soul, that to spare you I came not as yet unto Corinth.

  2. [2]
    Matthew 5:34-37

    But I say unto you, Swear not at all; neither by heaven; for it is God’s throne: Nor by the earth; for it is his footstool: neither by Jerusalem; for it is the city of the great King. Neither shalt thou swear by thy head, because thou canst not make one hair white or black. …

    Matthew 23:16-22

    Woe unto you, ye blind guides, which say, Whosoever shall swear by the temple, it is nothing; but whosoever shall swear by the gold of the temple, he is a debtor! Ye fools and blind: for whether is greater, the gold, or the temple that sanctifieth the gold? And, Whosoever shall swear by the altar, it is nothing; but whosoever sweareth by the gift that is upon it, he is guilty. …

    James 5:12

    But above all things, my brethren, swear not, neither by heaven, neither by the earth, neither by any other oath: but let your yea be yea; and your nay, nay; lest ye fall into condemnation.

Proof texts as given in the original; verse text from the King James Version.