What is a Christian?

We all do well to allow people to determine their own labels if we’re going to use religion labels. If a man says he’s a Christian, then we ought not to try to go behind his statement because we have particular beliefs about Christ with which he may not agree. “Judgment is mine sayeth the Lord.” He warned that many shall cry “Lord! Lord!” and many use his name to do miracles, cast out devils, but He shall say to them at the last days “Depart from me ye workers of iniquity, I never knew you.” Did He warn so we could judge and condemn others, or rather so that we could examine ourselves and be careful whom we follow?