Hebrews 6

Hebrews 6 speaks of the certainty of God's promises.  It is impossible for God to back on what he has said, impossible to lie.  Therefore, whatever God has said we can trust.  He never has gone against His word and he never will.  "So when God desired to show more convincingly to the heirs of the promise the unchangeable character of his purpose, he guaranteed it with an oath, ¹⁸ so that by two unchangeable things, in which it is impossible for God to lie, we who have fled for refuge might have strong encouragement to hold fast to the hope set before us." Hebrews 6:17-18