What does Galatians 3:9 mean?

Paul is making the case that we are saved exclusively on the basis of faith, not works. A group known as the Judaizers are trying to convince Christians that they must be circumcised and follow the law in order to be truly saved and included in God's family (Galatians 2:4). Paul has shown that even Abraham was justified—counted as righteous before God—because he believed the Lord, and not because he was circumcised (Galatians 3:6).

Now Paul wraps up this part of his argument about the children of Abraham. He states clearly that the blessing of God comes to those who believe God, including non-Israelites. He calls blessed Abraham the "man of faith."

It's important to notice two elements of Paul's argument: God's blessing and human faith. God's blessing can only be a gift, never earned by human action. In fact, it can be accessed only by faith in Christ.

Paul, sounding like a lawyer making his argument before a courtroom, will go on in the following verses to show why following the rituals contained in the Law can't save anyone. Paul is using his training as a Pharisee, one of the scholarly Jewish religious leaders. He is arguing from Scripture and logic, against the Judaizers, and in favor of the very truths for which he himself once persecuted Christians (Galatians 1:11–24).