The Second Man is First

I remember sitting in Greek class, working on translating passages from the Gospel of John, and reading John the Baptist's remarks about Jesus: This is he of whom I said, ‘After me comes a man who ranks before me, because he was before me.’ What caught my attention is that John is older than Jesus by at least six months. So, one might be puzzled when John states that Jesus is before John. Christianity stands or falls with understanding the person and work of Jesus (which seems like an obvious statement: no Christ, no Christianity). Therefore, I want to make a few comments on who this man is and why he is vital for Christianity.
Jesus is God the Son incarnate (which is a fancy word for "in the flesh"). He did not simply assume a body, but he took on human nature in such a way that he is both fully God and fully man. A denial of either of those points makes someone something other than Christian.
Jesus became incarnate in order to die in the place of man (as God stated that death is the penalty of sin). As God, Jesus could satisfy God for all people. If Jesus was not man, then he had no right to die in the place of man. If Jesus was not God, then, at best, he could only satisfy God for himself and no other.
The Christian faith is built upon Jesus being the Son of God, who died, was buried, and rose on the third day so that sinners might be reconciled to God.
Not to beat a dead horse, but a person cannot be a Christian by rejecting (1) Jesus as ever living, (2) Jesus as fully God (the same substance, not someone who became God), (3) Jesus died, and (4) Jesus rose bodily. That said, people may claim to be Christians, but they cannot be so if they deny any of the points laid out in the Nicene Creed. While Christianity is more than that, it is not less than that.