Something that I have been mulling around lately is what to call Christian. There were lots of Christians that we don’t call Christians today. They had some fundamental error in their doctrine that was not fit to teach. Shouldn’t we still label them Christians? I am not sure. How bad does your doctrine have to be for you to be expelled from Christianity Proper?
A case in point: the Gospel of Peter. The Gospel of Peter was wildly popular and while it contained some pretty bizzare miracles, the thing that got it expelled was its docetic implications. The early fathers were very concerned about people being mislead on matters of doctrine. Yet the people using the book considered themselves Christians and even the people that wrote the book considered themselves Christians.
My main question here is who should be called “Christian?” I say that the answer to the question on who is “saved” is reserved for God alone. What I am asking here, is who should we considered Christians and how do we relate with them and those that lie outside of that category? Since we cannot know the totality of the will of the father, how do we live this life down here?

For instance, is it all people who claim the title? Is it all people how can pass a multiple choice test? All people that act a certain way? Is it just people who act a certain way and can pass the multiple choice test?
One last question: “Should we use the category?” Should we treat all people the same and urge all towards right doctrine and right behavior? If so, how do you do that without alienating everyone? It is most certainly not productive to stand on opposite sides of the river and shout conclusions towards each other. If we all wade in and engage them as the equals we are (flawed humans seeking the truth), that might be the most productive.
I am not advocating any sort of relativity of truth here. I only want to perhaps suggest that we engage the other with out being condescending. I really don’t know what is the best way. I mean, say you are talking with a Mormon. This person truly and whole-heartedly loves Jesus and seeks to do his will. I consider the proper theology of the Mormon Church to be widely false and have huge doubts about the accuracy of the Book of Mormon. With that said, the mythical Mormon I am talking about might either be chosen by God as saved or is worshiping Jesus as he best knows and is trying to do His will.
How do I relate to this person, not shouting the conclusions to deaf ears and at the same time not alienate him?
I know this post is not written the best, but how do you deal with these questions/issues?