We have learned that the church of every age is plagued by false teachers and their deadly doctrine. We have met seven of those false teachers and seen the devastation they bring. We have identified five tests we can apply to any doctrine to determine whether it is false or true. But this leaves us with some important questions: How does a church come to reject sound doctrine? How do we guard ourselves against false teachers and their deadly doctrines? How do we protect ourselves, our families, and our churches from their seductive lies? Thankfully, God has given us clear guidance in his Word, showing us how churches descend into deadly doctrine and how we may protect ourselves against it.