All this talk of perfection really deals with the Christian doctrine of sanctification. When we accept Jesus Christ as our Lord and Savior, we are justified in God's eyes. Our sins are forgiven. We are saved. But salvation doesn't end there.
Salvation is a process.
After our baptism and confession of faith God becomes a part of our lives and helps us to grow in grace and love. Sanctification is the process by which we become more holy, more like God, as we grow in grace year after year. Our actions change, our attitudes change, the person we are changes to become more like Christ. For John Wesley, being perfect didn't have anything to do with making mistakes or not. We all make mistakes.