"We maintain that a person is justified by faith apart from works of the law." — Romans 3:28
Faith in Jesus comes as a gracious gift from God. Through faith imparted by the Holy Spirit, we are made right with God. In Romans 3 we learn what happens when we are given the faith to believe.
Paul lays out a tight argument on the movement from guilt to grace. He reminds his readers that the law revealed to God's people since ancient times does not save. The law convicts us of our sin. And, he exclaims, "All have sinned and fall short of the glory of God."
The good news, however, is that we can be made right with God (justified) through believing in Jesus Christ and being credited with his righteousness. Jesus stands in our place. His blood was shed for our sake, so when we believe (have faith) in him as the Savior, we are saved and made right with God.
Again Paul rejects any thoughts of bragging. We can't take any credit for becoming right with God. We only receive the saving power of Jesus' atoning sacrifice through God's grace, grace that extends even to the very act of believing and trusting (having faith) in Jesus.
God's astounding love and mercy bring us to our knees in awe and wonder. Paul himself exuberantly exclaims later, "Oh, the depth of the riches of the wisdom and knowledge of God! How unsearchable his judgments, and his paths beyond tracing out!" (Romans 11:33).