After proving that for the glory of God, salvation always had to be the work of God so it had to be by faith rather than by works, Paul now goes back to the covenant with Abraham. The Abrahamic covenant was made with Abram after he heard the promise of God that his descendants would be like the stars in the sky in number and believed Him. At ninety years old without offspring his whole life, it is easy to understand why Abram would not believe. According to the flesh, it made no sense. But Abram believed that the times were framed by the word of God, so if He spoke and said it would be so, then it would happen. He had faith and it was accounted to him for righteousness.