Worth remembering:
While genuine zeal in the discharge of one’s office is necessary and important, this cannot be said regarding any kind of zeal. There is a false, ungodly, carnal zeal that does not come from God and is not produced by the Holy Spirit, but is rooted either in animosity against those who teach a different doctrine or in the selfish thought that a display of zeal will bring the minister honor, at least in certain congregations, or in fanaticism.
– CFW Walther, Law and Gospel