We all know real money from fake by the way it feels , and bootleg dvds from the real thing. But how can we know what a true christian looks like , Christ tells us that we can.
5 This is the message we have heard from him and proclaim to you, that God is light, and in him is no darkness at all.
6 If we say we have fellowship with him while we walk in darkness, we lie and do not practice the truth.
7 But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus his Son cleanses us from all sin.
8 If we say we have no sin, we deceive ourselves, and the truth is not in us.
9 If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.
10 If we say we have not sinned, we make him a liar, and his word is not in us
(ESV)