What caused God to call Abraham a righteous man?
Paul says Abraham believed God, and it was his believing—not works or law—that caused God to call him a righteous man. Abraham did nothing to merit favor with God; his faith, not law-deeds, was the basis for being called righteous.
Les explains that by the deeds of the law no one can approach God on the merit of what they have done; God says we can do nothing to merit favor with Him. He then points to chapter 4 as plain proof: Paul says Abraham believed God, and it was his believing that caused God to call him a righteous man. So Abraham's righteousness was not earned by law-keeping but was the result of his believing God.