What did Paul mean by faith in Christ rather than just believing he was the Messiah?
Paul meant trusting in the finished work of redemption: that Christ died, was buried, and rose again. It is faith plus nothing, because the Law was satisfied and paid in full at the Cross. Believing Jesus was the Messiah belonged to Peter’s domain, not Paul’s phrase “faith in Christ.”
Les explains that Paul never speaks of just believing Jesus was the Messiah; that was Peter’s domain. When Paul speaks of faith in Christ, he means the finished work of redemption—Christ died, was buried, and rose again. Galatians 3 says believers become children of God by faith in Christ Jesus, not by keeping the Law. The Law has been satisfied, paid in full through the Cross, crucified and off the scene, so we enter in by faith plus nothing, all in the predetermined counsel of God.