A faithless christian is like a toothless dog. Abraham is called a friend of God simply because of his strong faith in God. He trusted God above all odds. He lived to see some of the promises God gave him though, he never saw the numerous descendants God promised him. Delayal for God's promises is not denial. Between God's promise and its fulfilment is opposition from the devil. Faith and patience will however help you to obtain it. Hebrews 6:12. Let us not be slothful, but let's be followers of those who through faith and patience obtain promises.
Talking of faith, even demons believe and tremble. The difference is, you don't have to give up.