In order to show that sinners are justified by faith (and not by works), Paul presents Abraham as a model of saving faith. In Romans 4:3 Paul quotes Genesis 15:6: “Abraham believed God, and it was credited to him as righteousness.” Then Romans 4:5 contains an interesting clause modifying “God”: who justifies the wicked.
Let’s draw a conclusion from Romans 4:3 and 5. If God justifies the wicked, and God justified Abraham, then Abraham was not justified because he was good. Abraham was justified in spite of being ungodly himself. Abraham, the man of obedient faith! Abraham’s ungodliness would be shocking to Jewish readers of Romans. Jews would not think that Abraham was ungodly or wicked. But such a Jewish misunderstanding empowers Paul’s argument: if Abraham must be justified because he was wicked and not already righteous, how much more do all Jews and Gentiles need justification!
Paul considers what would be true if Abraham was justified by his own works: “he had something to boast about” (Rom 4:2). Since only God can be credited with saving the sinner, boasting is excluded. Romans 3:28 affirms that “a man is justified by faith apart from observing the law.” So God prevents legitimate human boasting when it comes to salvation. If a believer tries to boast in his own works as the basis for his justification, he is a fool. It is sin to claim for oneself what belongs to God alone.
I’m thankful that Abraham was ungodly, aren’t you? Because God justifies the ungodly. And since you and I are ungodly (Romans 3:9-11), we can be justified through humble faith in Jesus Christ. We need to have the faith of ungodly Abraham.