But whatever was to my profit I now consider loss for the sake of Christ. What is more, I consider everything a loss compared to the all surpassing excellence of knowing Christ Jesus my Lord, for whose sake I have lost all things. Fanaticism and passion for God may appear superficially similar, but they are actually opposites. Saul was a fanatic until he came to know the living God personally. After he came to know God, he was passionate for God and the things of God.
Fanaticism is a type of sinful zeal.
It is essentially idolatrous. Its ultimate object is not really God, no matter what the fanatic may claim. Its object is glory and gain for self, not for God. It is not love for God, because the fanatic does not even know God. It is the best imitation of devotion that sinful man can produce.