Zeal must be based on intelligent understanding. It's in the Bible, Romans 10:2, NIV. "For I can testify about them that they are zealous for God, but their zeal is not based on knowledge."
Zeal should characterize spiritual life. It’s in the Bible, Romans 12:11, NIV. “Never be lacking in zeal, but keep your spiritual fervor, serving the Lord.”
Christ will make us full of zeal to do good. It's in the Bible, Titus 2:14, NKJV. "who gave Himself for us, that He might redeem us from every lawless deed and purify for Himself His own special people, zealous for good works."
Jesus cannot use us if we are complacent. It' s in the Bible, Revelation 3:15-16, 19, NKJV. “I know your works, that you are neither cold nor hot. I could wish you were cold or hot. So then, because you are lukewarm, and neither cold nor hot, I will vomit you out of My mouth....As many as I love, I rebuke and chasten. Therefore be zealous and repent"
Being zealous for God, means we take part in suffering for His sake. It's in the Bible, Psalm 69:9, NKJV. "Because zeal for Your house has eaten me up, and the reproaches of those who reproach You have fallen on me."