Wouldn't it be great if we could just throw open our arms and embrace anyone and everyone who claimed to be Christian. It should be like that but most of us know it isn't. So many people who claim to be Christian are stating their family tradition and not their personal relationship with Jesus. They haven't a clue what it is to live in the Spirit or to have anything to do with God except when they are in some kind of trouble. Even then the name of Jesus is used more as an exclamation than a plea for help.
This is why so many clarify their position in the Church with "born again" or "evangelical" or even "practicing". However, even these clarifications are not a measure for a personal relationship with Jesus. I am not talking about different subtleties in doctrine but the simple fact of a relationship with Jesus; a daily walking; Bible believing and living; Holy Spirit filled; Christ centered Christians. This is vital for us so we do not allow ourselves to be enticed away by those who claim Jesus but don't live Jesus. Paul warned Timothy:
But evil people who pretend to be what they are not will become worse than ever, as they fool others and are fooled themselves. (2 Timothy 3:13)
Is it possible to be evil and not realize it? Not at first, but I believe you can convince yourself that you are okay, that you are one of the good guys. When we tell the same lie often enough we start believing it to be true. Why would people do such a thing? Same motivation as there is for most sin: self-centeredness. There was something in the lie that profited the liar and so he kept on lying until he even believed it to be true.
There are a lot of pretenders in the Church who carry the title of Christian but have nothing to do with Christ. You will discover them by their actions. Without the Spirit of God it is impossible to carry on the act of Christ-like character for very long. You can see it in how they treat people. You will hear it in their language. You will detect it in the selfish attitude. It is possible to hide these things for a time but eventually the cracks start appearing. They will even convince themselves that unacceptable behaviour is actually acceptable and will convince others as well.
Again, this is the reason we must know Jesus, his character, his love, his mercy, grace, forgiveness. We must know it by experience and we must know it by the Word. We must know the authentic in order to recognize the fake. We must do this more and more as the days grow darker and the influence of evil grows bolder. I am not talking about going on a witch hunt; that is not our responsibility. I am only talking about being able to recognize the authentic to embrace and the false to avoid. God will take care of the wheat and the weeds, we just need to test the spirit in all things.
Don't be fooled by those who have fooled themselves. Anyone can be persuasive; all they have to do is truly believe what they are saying. But words alone are not how we test the spirit. Following Jesus is not an academic exercise but living the character of Jesus 24/7 by the power of the Spirit in us. Please be careful, it is getting dangerous out there.