We say that a person filled with excessive zeal, especially for an extreme religious cause, is a fanatic.
If you are always in religious garb, pining for your next moment to pray or supplicate, choosing your foods according to religiously approved dietary rules, avoiding music and dancing because it’s too worldly, pining for the day when the world bows before the dictates of your religion, or comes to a fiery end, then you are a fanatic.
freedom and reason 