Guaranteed Purpose

Because God wanted to show His unchangeable purpose even more clearly to the heirs of the promise, He guaranteed it with an oath, so that through two unchangeable things, in which it is impossible for God to lie, we who have fled for refuge might have strong encouragement to seize the hope set before us. We have this hope—like a sure and firm anchor of the soul—that enters the inner sanctuary behind the curtain. Jesus has entered there on our behalf as a forerunner, because He has become a “high priest forever in the order of Melchizedek.”
(Hebrews 6:17-20 Holman Christian Standard Bible ®©)