During a legal trial, those testifying about what they saw take an oath to tell the truth, the whole truth, and nothing but the truth. They swear by God, saying “so help me God.” (Or at least they used to, I think the oaths may exclude that these days.)

Now in Hebrews 6:17-18 we read, “In the same way God, desiring even more to demonstrate to the heirs of the promise [that’s us] the fact that His purpose is unchangeable, confirmed it with an oath, so that by two unchangeable things in which it is impossible for God to lie, we who have taken refuge would have strong encouragement to hold firmly to the hope set before us.” (NASB 2020)