Whichever person that is born of God does not consign sin….” (1 John 3:9 says) Some people don't understand this they and ran off with the bad idea that anything they do is right, because as Christians, they can’t commit sin. Yes, for the Christian, sin is not necessary, but we do not judge being righteous by what a Christian does; righteousness is judged by the light of Christ and His Word. In 1 John 1:7 The scripture talks about walking in the light of God as God is in the light.
How regular are your actions with the correctness of God? That’s the way you know what is right from what’s not right. If you disclose that anything you do is right, that makes you the standard of correctness and of holiness. But you are not the righteousness standard. For instance, in 1 Corinthians 2:16, it's written that we have the Christ's Mind. This does not mean all thought of your heart, is right always. Yes, we have the correctness of God, but He let us know not be conformed to this world, but be transform by the renewing of your mind.”(in Romans 12:2)
Even if you are born again, you still need to renew your mind. 1 John 2:1 say “My little children, these things that I write unto you, that you don't sin….” If it is not possible for you to commit sin against Him, He would not have tell us that: “ so that you don't sin.” But all the same, He still make us aware that sin isn’t necessary; you have to commit sin. That is the reason why for the next remark: “If any man commit sin”; instead of “When any man sins.” He makes a balance.
Don’t go from one excessive of “Sin is necessary so far we are in this flesh” to the other excessive of “everything I do is right”; no! Your thoughts, actions, behaviour, how you make responses and your reactions have to be regular with the Word of God, with Christ's righteousness because He is the standard of righteousness.