Hebrews 6:16-19

When people make vows, they use the name of someone greater than themselves, and the vow settles all arguments. To those who were to receive what he promised, God wanted to make it very clear that he would never change his purpose; so he added his vow to the promise. There are these two things, then, that cannot change and about which God cannot lie. So we who have found safety with him are greatly encouraged to hold firmly to the hope placed before us. We have this hope as an anchor for our lives. It is safe and sure, and goes through the curtain of the heavenly temple into the inner sanctuary.