Thomas Brooks warns against the dangers of unholy ministers, emphasizing that their sinful lives can lead their congregations down a path of destruction. He argues that an unholy preacher not only undermines their own doctrine but also serves as a poor example, causing their hearers to stray from holiness. Brooks stresses that the moral integrity of a minister is crucial, as people are more influenced by their actions than their words. He concludes that the unholy lives of ministers can significantly hinder the pursuit of holiness among their followers.