Hebrews 6:16-19

People always use the name of someone greater than themselves when they swear. The oath proves that what they say is true. And this ends all arguing about what they say. God wanted to prove that his promise was true. He wanted to prove this to those who would get what he promised. He wanted them to understand clearly that his purposes never change. So God proved his promise by also making an oath. These two things cannot change. God cannot lie when he makes a promise, and he cannot lie when he makes an oath. These things encourage us who came to God for safety. They give us strength to hold on to the hope we have been given. We have this hope as an anchor for the soul, sure and strong. It enters behind the curtain in the Most Holy Place in heaven.