Is that a sufficient definition of what a Christian is?
Twenty years ago, I think I would have said, "Yes."
What happened to me was an increasing disquiet about what constituted faith and belief. I could say that I believed this, that and whatever the church I was in at the time believed; yet there were questions, including inconvenient passages of Scripture, that would not go away.
Then there was the question of history; that is, whence the beliefs that I am embracing; what is the source?
What was going on in the Protestant Reformation? And the Anabaptists were a whole different matter. Everywhere I looked, I saw men taking what had been passed down and re-forming and sometimes attempting to re-make it.
To make a long story short, I came to the point that I needed an objective standard, outside of myself. This leaves me with one of two choices - the Roman Catholic or the Orthodox Christian Church. In both, I find legitimate claims to preservation of the faith once delivered to the saints.
The differences between those two are minor, compared to the lack of coherence and the additions/subtractions that I was seeing in other Christian traditions.
So, what is my definition of Christian? The Catholic teaching I believe, speaks of those joined "imperfectly" to the Catholic church. Many share a few, several, or many beliefs, but depart on some. There is the "imperfection." The Orthodox generally lack definitive teaching in the same manner, but, I believe are in general agreement. Both can define who they are and who are theirs. They do not judge on who are not theirs.
So, who and what are Christians? I cannot say. But, I return in my mind, to the scene related by Jesus in a parable of the Final Judgement and the surprise of both those who are and those who are not received into the Kingdom. I'll probably be surprised as well.
I look at all Orthodoxy as bordering on sin, if is it the practice of things we do to earn what is already dearly paid for. We all die alone, facing the Throne, so to speak, without our orthodoxies, but assessed by what we did with so great a gift, the knowledge imparted to us. I don't forsake the assembling of ourselves together, and I act daily in the light of what I believe about Christ and the World. This cannot help but make us a contrast with the great sea of others who are not so gifted. We have accepted the Word defined. I love the Catholic orthodoxies, but need no intercessor between God and me aside from Christ. I cvan't merit the unmerited favor of Christ, a gift made possible by the infinite value of his perfect sacrifice. Neither, among the others, can I gain access to God through behaviors, which are putting the cart before the horse, it seems to me. Faith is action based upon belief, I believe. Our behaviors just can't be the same as they were before we came to accept the overwhelming evidence of that what Christ did for us can't be earned or bought. "It is finished," he said, before yielding up the spirit. And the curtain separating the Holy of Holies in the Temple rent in two, from the top to the bottom, and not the other way around.