David McCullough in his book Mornings On Horseback tells this story about young Teddy Roosevelt:

Mittie (his mother) had found he was so afraid of the Madison Square Church that he refused to set foot inside if alone. He was terrified, she discovered, of something called the "zeal." It was crouched in the dark corners of the church ready to jump at him, he said. When she asked what a zeal might be, he said he was not sure, but thought it was probably a large animal like an alligator or a dragon. He had heard the minister read about it from the Bible. Using a concordance, she read him those passages containing the word ZEAL until suddenly, very excited, he told her to stop. The line was from the Book of John, 2:17: "And his disciples remembered that it was written, 'The ZEAL of thine house hath eaten me up.'"

People are still justifiably afraid to come near the "zeal" of the Lord, for they are perfectly aware it could "eat them up" if they aren't one of His. Our Lord is good, but He isn't safe.