Statesboro, GA, USA
Well Ess, here's the thing. I have often said that I am an agnostic Christian. What does that mean? It means that my ethical system is derived from the Christian heritage that surrounds me -- but that I don't adhere to, or require any supernatural belief in order to enact that ethos.
Think of it like this, there are John 3:16 Christians -- who would dwell on the deity of Jesus.
I am a Matthew 25:31-46 agnostic Christian
Yeah, what does that mean?
I think you would do better to merely say "I'm not a Christian. But I'm a moral person", than to reconstruct the meaning of the word "Christian". Of course the word has already been stretched (extra-Biblically) to mean many things, but your statement goes beyond even these.
Following an ethos that merely "surrounds" you, is not necessarily a virtuous claim. It does fit the egoistic "contract theory" of Lock and others, but doesn't deserve the epithet "Christian". Besides, Jesus did not exactly establish any new ethos at all. The ethical insight of Pagan philosophers, and religions, before him, had the right ethos. If anything he only amplified the signal ... widening the jurisdiction of the law, rather than changing it's personality. Just read the appendix in C.S. Lewis' "Abolition of Man", where Lewis presents a basic harmonization of ethical systems, to show that they are more alike (and have always been so) than people admit. So is the approval, and sporadic practice of a prevailing ethical system "enough" to call yourself Christian? There are some things Guatama said that I respect, recognize as truth, and practice, but I don't call myself a "Christian Buddhist". I am a Christian. You are an agnostic.
The thing is, is that Jesus himself never made a distinction between any "kinds" of Christians. John 3:16 and Matthew 25:31-46 give us elements of the same whole. The agnosticism of Matthew 25 is not about who Jesus himself is, (those being judged call him 'Lord'), but of the nature of the forgotten recipients of their kindnesses. The agnosticism that is illustrated, is of the organic connection between their good works to the "common" needy people in life, and the God that they worship who is anything but common. This is seen elsewhere in Jesus' teaching where he said "don't let your left hand know what your right hand does" (Matthew 6:3). That can't be interpreted as, "it's not necessary that both hands serve God".
So on scripture's own terms, in context, this is not the definition of a "Christian". Who Jesus is is always central to that definition. Without it, you have an ethos which is neither new, or greatly different from what has always been. There have always been moralizers. Now whether those moralizers have had a rational reason behind their morals beyond social contracts and egoism, is another question. Without God, I don't think so. For true morals will always, at some points, contradict self interest, and the "crowd" mentality. It will cause you to deny both yourself and the mob. And without an ultimate judge, who represents more than human subjectivism, all ethical systems are doubtful.