Hebrews 6:17-18

God wanted to prove that his promise was true to those who would get what he promised. And he wanted them to understand clearly that his purposes never change, so he made 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.