Rom 13:9 For this, Thou shalt not commit adultery, Thou shalt not kill, Thou shalt not steal, Thou shalt not bear false witness, Thou shalt not covet; and if there be any other commandment, it is briefly comprehended in this saying, namely, Thou shalt love thy neighbour as thyself.
Rom 13:10 Love worketh no ill to his neighbour: therefore love is the fulfilling of the law.
4 Whoever says “I know him” but does not keep his commandments is a liar, and the truth is not in him,
5 but whoever keeps his word, in him truly the love of God is perfected. By this we may know that we are in him:
Isn't that saying that the only sin that could be committed by such a person is a sin that a) does not work ill to his neighbour, and b) does not break any commandment of God. What sin is that?
1Jn 3:4 Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law.
It is clear that we all have sin. We should not think that we have not sinned. But neither should we think that our sin cannot be cleansed, or that our sinfulness cannot be put to death. Jesus died to take away the sin that we are guilty of, and he makes his abode in us to take way our sinfulness.
Rom 5:10 For if, when we were enemies, we were reconciled to God by the death of his Son, much more, being reconciled, we shall be saved by his life.
Gal 2:20 I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me.
If we sin, we have an advocate with the Father, to plead with us, and to comfort us, and to show us hope. But there comes a point in time when we have learned and have faith, such as Jesus had. His faith kept him from sin. And as it is written "We have the mind of Christ."