The perfect work of Jesus is enough, and it is not your actions that save you. However, if one is to overcome sin and the devil, if one is to be made like Jesus, the reading of His Word and prayer(Luke 22:32)(Mark 9:29) is mandatory. Because you need God to be like God. Your obedience requires Him. And any moment that you spend following Him in your own strength is not obedience, but disobedience in legalism. I’ve heard from some men that there is a fear of success by one’s own strength that leads to a trust in one’s own abilities rather than in God. Because such success leads to faith without God and belief in one’s ability to follow Him. How is that not prideful? (James 4:6) How does that lead to someone affirming that apart from God we can do nothing? (John 15:5) Yes, you don’t need to do anything if you’re a Christian, because of the perfect work of Jesus. But to live as a Christian, you most certainly need God.