Years ago a friendly exterminator patrolled some neighborhoods in Chicago, peddling what he called “the Mississippi stuff.” The Mississippi stuff was a pesticide he had bought hundreds of gallons of in the South, and it really did the trick on cockroaches. The exterminator went door-to-door with his hand sprayer, and his business grew as satisfied customers recommended his remarkably effective work to all their friends and neighbors.

In the process, however, this one pest control specialist is alleged to have single-handedly created an environmental catastrophe. The effective pesticide—methyl parathion—is outlawed by the EPA for use in homes. Southern farmers use it on boll weevils in their cotton fields, and within days the pesticide chemically breaks down into harmless elements. Not so in the home. There the pesticide persists as a toxic chemical that can harm the human neurological system with effects similar to lead poisoning.

When the problem was recognized, the EPA was called into Chicago for the cleanup. Drywall, carpeting, and furniture sprayed with the pesticide had to be torn out and hauled to a hazardous-materials dump. The U.S. Environmental Protection Agency estimated that the total cost of the cleanup would be some $20 million, ranking this as one of the worst environmental nightmares in Illinois history.

The exterminator was charged with two misdemeanors. He apparently didn’t know much about the pesticide he sprayed so liberally. His attorney said, “It’s a tragedy. It is one of those situations where he did a lot of harm, but his intention in no way matches the damage he has done. He is a family man and handled it with his own hands. Do you think he knew how toxic it was?”

What you don’t know can hurt you. That is true both of pesticides and of false teaching. Some have said that it doesn’t matter so much what you believe as long as you are sincere. Nothing could be further from the truth! Many people in Chicago believed that they were getting rid of roaches without risking the health of themselves and their families. They were wrong. Tragically wrong in some cases.

Jesus warned against false teachers. In Matthew 7:15 he says, “Watch out for false prophets. They come to you in sheep’s clothing, but inwardly they are ferocious wolves.” The letters to the churches are filled with admonitions to avoid false doctrine and to rebuke those who teach it. Titus 1:11 says, “They must be silenced, because they are disrupting whole households by teaching things they ought not to teach—and that for the sake of dishonest gain.” 2 Timothy 2:17 warns, “Their teaching will spread like gangrene…”

So, it does matter what you believe, and what you don’t know can indeed hurt you. False teaching can cause great damage to individuals, families and entire congregations. Learn the truth and stick to it! Avoid false teaching at all costs!