Most people who are apart of a religion think they have the true religion. Or at least they should. Why be part of a religion if you don't think they have the truth? I suppose some join just for the social aspect of it all but that was not what Jesus taught.

The first century Christians definitely had the truth. Nothing wrong with those who are trying to follow the first century Christians to believe they have it either. And maybe they don't have 100% of it but they have more than any other religion I have seen to date.