I may not have understood him correctly but this is one of the doctrines he had to defend most vigorously. As a painter that took pride in my work, for a time I was a perfectionist. I kept on doing the best I could but to be perfect was not ever something that I could attain, so it just frustrated me. If I were to expect that within myself, I would have to expect it from those under me in my employ and that would not be right. We are however told to be perfect, so we do the best we can in what we do and at least have perfection in mind even though we fall short.
Grace is different.
With grace, God makes us perfect when we are not. Paul had that thorn in his flesh, whatever it was is not important but it taught him about grace. We are perfect in God's sight but for me, I do not think I ever will see it until Jesus comes for me. Maybe, I should think differently and of course there are times in my life when I do sin and have to ask for forgiveness. God is faithful to forgive me and I can only praise Him for it.