Hebrews 6:16-18 Easy-to-Read Version (ERV)
16 People always use the name of someone greater than themselves to make a promise with an oath. The oath proves that what they say is true, and there is no more arguing about it. 17 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 said something would happen, and he proved what he said by adding an oath. 18 These two things cannot change: God cannot lie when he says something, and he cannot lie when he makes an oath.
So these two things are a great help to us who have come to God for safety. They encourage us to hold on to the hope that is ours.