Definition of a Christian Revisited
Allow me to step back from the project for a bit and look at what is foundational to it.
The believer in the Christian faith is primarily a believer in a particular cosmology. It is characterized by a Triune God, invisible/non-corporeal beings (primarily angels and demons), humans (that is, corporeal beings with a soul… halfway between spirits and beasts), beasts, and inanimate created things. It is in examining the relationships one has with each of these beings or created things and that each has with every other that we come to understand morality, etc.
Now, the primary relationship anything has is with the Triune God, who created all things, and is therefore the source of every relationship. That is, all other relationships flow from and are necessarily related to every thing’s relationship to the Triune God. If one’s relationship to God is correct, one’s relationship to all other things will also generally be correct, plus or minus a few degrees of error. Thus, it makes sense that the definition of a Christian should outline who their God is, how he interacts with men and how men should interact with him.
When I first proposed a definition, a few of you were very correct in suggesting that I include the incarnation, as a (the) significant event in God’s dealings with men. When I said that “Christians are people in communion with the God who…”, I was undertaking the right project (that of identifying the God), but my identifiers were incomplete. The fact is that there are things we know about our God that to deny would be to reject the Christian God. These must all be laid out in the definition of a Christian since such a definition is primarily the description of a relationship with that God. Thus, I am convinced that even the incarnation was an insufficient identifier.
In this identification, the fact that God is a Trinity must be included, the fact that the second person of the Trinity, the Son, came down to earth and became a man, Jesus Christ, fully God and fully man, one person with two natures, must be included. We must say that to be a Christian is to be in communion with God, the Father (creator, unbegotten), Son (Word, Jesus Christ, by whom all things were made, begotten of the Father), and Holy Spirit (proceeding from the Father, revealing the things of God to men), with the Church, etc.
Now, hold on, you will say, you are just saying the creed, or something very like it. And I would say, yes, I realized the same thing… eventually. My big definitional project was actually (or more properly) the pursuit of a Christian creed. You may imagine that I felt a little foolish on realizing that. The fact is, we have a number of good ones already. The time may have come to formulate a comprehensively acceptable one, but I am rather think that we should be able to use the ones we have.
In short, the moral of the story is, go out and read the creeds. Memorize them; hold them close. If you disagree with them, it is likely that you have a smudge of heresy and should go find your local Christian theologian to help you expunge it. The creeds are what bind us together.