One of the characteristics of God given repentance is zeal, a passionate enthusiasm in the pursuit of something (1Corinthians 7:11). Zeal can be either good or bad, it just depends on what you are passionate about and how you pursue it. Maybe the best example of how that works is Saul of Tarsus. He was a zealous man. He was passionate in what he believed and pursued his goal with full force. Early in life, he was zealous in his Judaism to the point he persecuted anyone who disagreed (Philippians 3:6). Then, he met the Lord Jesus and was born again. After he was saved, Paul mellowed out and realized being balanced and moderate was the best way to win the culture for Christ. Just kidding. Paul was more zealous as a preacher of the gospel than he was as a hit man for the Pharisees. Christ didn’t take away his zeal, he sanctified it and used it in the right way for the right reasons. Paul's zeal was guided by Christ, and for Christ. And it got him in trouble, just with a different group of people. The apostles could have quietly worshiped Jesus in their homes, as long as they didn't mention the name of Jesus publically. But how could they not tell about what they saw and heard? Their zeal for something good got them in trouble (Acts 4:17-20).
Zeal can be thought of as a fire, it can be good or bad. Fire can keep you warm and cook your food, but out of control and undirected, it can also burn down a forest. Wild, out of control passion without guidance and direction is dangerous. Passionate enthusiasm isn't always a good thing. Years back, I was down south on a trip and enthusiastically making my way back home on the interstate. I made a quick pit stop and got back on the road. An hour later, I realized I was driving the wrong direction. My zeal for getting home didn't change the fact I was going the wrong way.
In John 2:13-17, Jesus was righteously angry at the wicked men dishonoring his Father’s House. They turned a house of prayer into a den of thieves. His love and desire for the glory of His father and his indignation at this wanton sinfulness is displayed in his zeal by crafting a whip and running out the money changers. Jesus didn’t lose his cool. He wasn’t controlled by his emotions, but a true human man could not stand by idly and watch this wickedness without being zealous for the cause of God. Isaiah 9:7, “Of the increase of his government and peace there shall be no end, upon the throne of David, and upon his kingdom, to order it, and to establish it with judgment and with justice from henceforth even for ever. The zeal of the LORD of hosts will.” The opposite of fanaticism isn't stoicism. Christian, you need to be zealous for the glory of God.