What does Romans 4:3 mean?

Paul is making a case that no human being has ever been justified—made right with God—by following the works of the law. This is primarily aimed at Jewish readers and those who have heard the arguments of the Jewish religious leaders.

Now he points to Abraham as a prime example, using Old Testament Scripture as his source. According to Scripture, Abraham was not justified by what he did: by his works. Instead, God credited Abraham as righteous when he believed and for believing (Genesis 15:6). It was faith in God, not his own works, which allowed Abraham to be justified before God.

Paul made this very same argument to the Christians in the region of Galatia (Galatians 3:6). They were being persuaded by a group known as the "Judaizers" that they must be circumcised and follow the law, in addition to believing in Christ, in order to be truly saved. Paul used the example of Abraham in that letter, as well, to show that this argument was false.