18Against all hope, Abraham in hope believed and so became the father of many nations, just as it had been said to him, "So shall your offspring be." 19Without weakening in his faith, he faced the fact that his body was as good as dead—since he was about a hundred years old—and that Sarah's womb was also dead. 20Yet he did not waver through unbelief regarding the promise of God, but was strengthened in his faith and gave glory to God, 21being fully persuaded that God had power to do what he had promised. 22This is why "it was credited to him as righteousness." 23The words "it was credited to him" were written not for him alone, 24but also for us, to whom God will credit righteousness—for us who believe in him who raised Jesus our Lord from the dead. 25He was delivered over to death for our sins and was raised to life for our justification.
Faith is simply believing that God is able to do what he said he'd do. Abraham believed that God would give him a son through Sarah. He believed, hope against hope. Sarah was old, her womb as good as dead. Scientifically there was no chance of her conceiving. But God said she would have a child and so Abraham went out and bought a pram.
This simple belief in him is what God likes. When God says something he wants us to believe it, just like a child believes what his parents tell him. It is not moral uprightness or anything else that God wants from us, it's belief: being fully persuaded that God is able to do what he promised, and is committed to doing it. Such belief was righteousness for Abraham and it is righteousness for us, too.
I've made it this far with sentences and paragraphs. Time for a list.
Six thoughts about faith
1. It's relational. We believe that what God says will happen, will happen, because we trust him. We know he is powerful so able to keep his promises. We know he is true so he will keep his promises. Faith is tied up in our relationship with God.
2. It's concrete. 'I believe in God' can seem really nebulous. You mean you believe in the existence of God? Which god? Does that have any real connection with life? Christian faith in Romans 4 is concrete. God has said specific things. We believe them.
3. It is salvation focussed. Primarily we believe what Abraham believed: that God is able to bring life from the dead. He brought life from Sarah's dead womb, beginning salvation for the world. We believe that he raised Jesus to life ensuring our forgiveness. The bulk of the promises God has made concern the salvation of the world. At the center of our faith is our belief that God will right the tragedy of the fall and redeem us for a new creation. There are other promises (God never leaving us etc) but these fit in around the bible's central salvation focus.
4. It has always been God's way. God has always commended people for faith. Unfaith was the sin of Adam and Eve. Faith was the strength of Noah, Abraham, Isaac, Jacob, Moses, Rahab, Joshua, David etc.
5. It's comforting and burden lifting. I don't need to do stuff. I can rest confident. I believe that God is able to do what he promised.
6. It issues in action. Believing that God's word is true will cause us to live differently. Noah built a boat. Abraham left Ur. Jesus allowed himself to be nailed to a cross. If I believe that what God has promised will happen, I will spend my time and money differently to someone who doesn't believe it. I will think differently. I will do different things. God has made some pretty big promises for future events. If it's not making a pretty big difference, then maybe I don't really believe it.