Repentance involves a change of mind and direction. There were times in the Old Testament where God changed His mind and repented either of a judgment He was going to bring on a group of people, or, in the case of King Saul, repented that He had made him king. It was not because God had sinned in any way. It was that He reversed a previous decision and changed His direction about how He was going to act in a particular situation.
Repentance for the unbeliever is a change of attitude toward Christ and a change of direction from a life of rebellion against God to a life glorifying to Christ. The use the word repentance to describe a sorrow for sin and the desire to stop sinning, it not quite an accurate application of the word. Repentance happens only once. It happens at conversion.
At conversion our sin is taken from us and put on the cross with Christ, and then buried in the deepest sea of God's forgetfulness never to be revisited. We are then given the righteousness of Christ which makes us perfect in God's attitude to us. That is the perfection that God requires of us.
If we try and be perfect in our own strength, we are acting in unbelief and trying to be self-righteous, which is like a filthy rag in God's sight. Perfection is trusting in the righteousness of Christ which has been given to us by God's grace through our faith in Christ. Along with that, we have been given a new heart that gives us the strong desire to overcome our sinful habit patterns with the help of The Holy Spirit, and to live a life glorifying to Christ.
