Yes, God certainly wants us to repent of our sins and begin living the way we should when we come to Christ. Repentance and faith go together, and both are essential. In His first recorded sermon, Jesus declared, "The time has come.... Repent and believe the good news!" (Mark 1:15).
But you're right: We aren't perfect. The problem is that we don't have the inner strength to live the way we should. Our old sinful, self-centered nature still lives within us, and it constantly tries to pull us away from Christ. In addition, Satan will do everything he can to turn us away from Christ. Even the apostle Paul experienced this struggle: "What I do is not the good I want to do; no, the evil I do not want to do -- this I keep on doing" (Romans 7:19).
Does this mean it's hopeless to try to live for Christ? No, certainly not. The reason is because Christ now lives within us by His Holy Spirit, and He will help us overcome temptation. We don't have to fight the battle alone! The Bible says, "The Spirit helps us in our weakness" (Romans 8:26).
When temptations come, turn immediately to Christ and seek His help. Don't let the temptation take root in your mind and heart; reject it at once, and turn it over to Christ. Then trust God's promise to help you and strengthen you through prayer, fellowship with other believers, and the truth of His Word, the Bible.