Our understanding of what a true Christian is, comes from the Bible. In the New Testament Gospels, Jesus describes a follower of His as a disciple.  A disciple is one who lives according to the example, modeled by the One he follows.  A disciple the teachings and obeys the commandments of the One he follows. 

In order to follow Jesus, as His disciple, we need a power to enable us to do so, that is beyond our natural ability and understanding. Jesus doesn't call us to be religious. He calls us to become like Him. To do that, we need a brand new nature. The only way to receive that new nature is to believe God to do something He has promised He would do for all who desire Him to. He will give us that new nature. It comes to us through a New Birth! The new nature comes to us by the Holy Spirit and is something that God Himself imparts to us. This is why the Bible calls it, a New Birth! It is a new beginning! This is how we receive the new nature we need to follow Jesus' teachings and obey His commandments.