Hebrews 6:13-17

13Now when God made His promise to Abraham—since He could swear by no one greater, He swore by Himself,

14saying, “Surely I will bless you, and surely I will multiply you.”

15And so after waiting patiently, Abraham reached the promise.

16For people swear by someone greater; and the oath, as confirmation, is an end to all their disputing.

17In the same way God, determining to point out more clearly to the heirs of the promise the unchanging nature of His purpose, guaranteed it with an oath.