Who are we that God should make a promise to us?
When God made the promise to Abraham, since he had no one greater by whom to swear, “he swore by himself,” and said, “I will indeed bless you and multiply” you. And so, after patient waiting, he obtained the promise. Human beings swear by someone greater than themselves; for them an oath serves as a guarantee and puts an end to all argument. So when God wanted to give the heirs of his promise an even clearer demonstration of the immutability of his purpose, he intervened with an oath, so that by two immutable things, in which it was impossible for God to lie, we who have taken refuge might be strongly encouraged to hold fast to the hope that lies before us. -Hebrews 6:13-18, NAB
When we make a promise, or an oath, we do so before God. For instance, prior to taking the stand at a trial, we make an oath to tell the whole truth, and nothing but the truth. But how is God involved in all of this?
The point is that our promises mean very little. We are weak, frail creatures, and we are quick to break our promises. So when we truly want to guarantee someone that we will not break that promise, we take an oath before God that our words are true.
To follow that pattern, God offered an oath to Abraham, saying that He would bless Abraham’s descendents. God also made a promise to us through His Son, Jesus Christ, that if we have faith in Him, we will, one day, find salvation.
God, of course, can never fail. He does not need to invoke anyone else’s name when He makes a promise. What is the purpose of God’s oath to us, then? To give us peace of mind. He wanted to let us know, without a doubt, that this promise would come true.
God’s oath, His promise to us, gives us hope in a fallen world. His promise to Abraham has come true, and we can rest assured that His promise to us, our hope of salvation, will come true, as well.