Actually nothing changed the law. What changed was God's covenant with man upon the death of His Son, Jesus Christ (Heb. 8:6-13). The Bible says the law is "holy, just, and good" (Rom 7:12). The problem is with man - he can't keep the law and was never meant to. The law came about to expose man to his absolute shortcomings. "Wherefore, the law was our schoolmaster to bring us to Christ, that we might be justified by faith" [not works] (Gal. 3:24). The problem with the law is it can't fix anyone (Heb 7:19), it can only condemn.
Jesus (not Paul) changed everything, not by abolishing the law, but by fulfilling it for us (Matt 5:17). We are no longer under the law (Rom 6:14). Jesus did what we could never do. So becasue of Jesus, we are righteous, accepted, forgiven and victorious, not because of our works, but because of His works. Hallelujah! THAT is the gospel of the grace of our Lord Jesus Christ. Shout it from the mountain tops.