'Oath' in the Bible

For men indeed swear by a greater, and with them the oath is a term to all dispute, as making matters sure.

Wherein God, willing to shew more abundantly to the heirs of the promise the unchangeableness of his purpose, intervened by an oath,

And by how much it was not without the swearing of an oath;

(for they are become priests without the swearing of an oath, but he with the swearing of an oath, by him who said, as to him, The Lord has sworn, and will not repent of it, Thou art priest for ever according to the order of Melchisedec;)

For the law constitutes men high priests, having infirmity; but the word of the swearing of the oath which is after the law, a Son perfected for ever.