Hebrews 6:16-18 NLT
[16] Now when people take an oath, they call on someone greater than themselves to hold them to it. And without any question that oath is binding. [17] God also bound himself with an oath, so that those who received the promise could be perfectly sure that he would never change his mind. [18] So God has given both his promise and his oath. These two things are unchangeable because it is impossible for God to lie. Therefore, we who have fled to him for refuge can have great confidence as we hold to the hope that lies before us.
The truth is, we all understand the concept of people taking oaths and how that oath guarantees they will keep their word. Isn't it strange then we question whether God will keep his word to us despite the fact his word is back by both his promise and his oath. God is essentially saying, 'if I fail to keep my word to you, then let God punish God'.
We can be sure, God's word can never fail.