The bare minimum, to me, for someone to belong to the Christian religion is for them to worship Jesus Christ in any way or form. They don't have to consider him a god, or attempt to act like him, but they have to worship him in some spiritual way. People might be moral or philosophical Christians if they try to emulate Jesus but don't have the worship element, but that won't cover the religion aspect to me. Likewise, acting according to a particular moral structure is something that most Christians (religious version) follow, but it's not necessary for them to fit the definition. It's the same way that a Zeusian would be a Zeusian no matter their moral structure, because they worship Zeus and that's all the word means.