A Christian is not somebody who follows the ethical and moral structures of Jesus, because a person can do this and still deny that Jesus Christ is the eternal God in the living form. It’s done all the time. There are people all over the world following morality and ethics very close to Christianity who are not Christians. What we have to do is determine how to define words “Christian”. For that we must to go to the scriptures.
A “Christian” in the New Testament is somebody who believed that Jesus Christ was the Messiah of Israel and the savior of the World; that He died on the cross in the place of our sins; that His blood is atonement for our sins; that He rose bodily from the grave and ascended to heaven; and that He will come again to judge the living and the dead.
A great quote by Dr. Walter Martin, “A Christian is not defined by the life lived, but the beliefs believed. Therefore while a certain type of behaviour flows, from the Christian’s beliefs it is not the behaviour but the beliefs themselves that define what a Christian is.”
Source: Dr. Walter Martin, Martin Under Fire, Audio Tape #4