Even if a person happened to be perfect in all his thinking and actions, he would still have genetic "sin," handed down from his parents. Perfection is necessary, because even the least imperfection is not good enough for God.
The only perfection that is good enough is Jesus-perfection. Jesus was perfect in every way. He applies His perfection to us, if we accept it. That's the only way to get to Heaven.
The major repentance is to repent from unbelief to faith in Jesus salvation.
Secondary repentances are to do the things that Jesus wants through that faith, and out of love. The greatest command is, "Love God above all things." The second command is, "Love other people as you love yourself."
Perfection was done by Jesus. His application of perfection to us depends on the strength of our faith in Him. However, once we belief in Him, He will hold us strong enough in that faith to be saved. Our good works will never be technically good enough. But they will get better through our faith in Jesus.
Anybody who thinks that he his saved by faith in Jesus, and then goes out and does bad things to other people, while trusting that he will be forgiven, is destroying his own faith in Jesus salvation. At some point, Jesus will let him go. Then, there will be no turning back for him. Don't test God that far.
