Hebrews 6:17-18 with commentary:
In the same way (as people sware to back up their words) God, desiring even more to show to the heirs of the promise (that’s us!) the unchangeableness of His purpose, interposed (confirmed) with an oath, so that by two unchangeable things in which it is impossible (literally cannot happen) for God to lie (to lie or deceive), we who have taken refuge would have strong encouragement to take hold of the hope set before us.
So in case you ever wondered how serious God is about us knowing His steadfastness, know that He went to ridiculous lengths to show us His faithfulness and guarantee His own character. All so that we can have the courage to actively take hold of the hope set before us. He knew we would need it!