Convert.
Synonyms:
disciple, neophyte, proselyte.
The name disciple is given to the follower of a certain faith, without reference to any previous belief or allegiance; a convert is a person who has come to one faith from a different belief or from unbelief. A proselyte is one who has been led to accept a religious system, whether with or without true faith; a convert is always understood to be a believer. A neophyte is a new convert, not yet fully indoctrinated, or not admitted to full privileges. The antonyms apostate, pervert, and renegade are condemnatory names applied to the convert by those whose faith he forsakes.