Charles Finney warns about the dire consequences of spiritual relapse, using the metaphor of an unclean spirit returning to a man who has not filled his heart with righteousness. He illustrates how the Jewish nation, after a brief awakening under John the Baptist, fell back into deeper sin upon rejecting Christ, leading to a state worse than before. Finney emphasizes that a temporary absence of evil does not guarantee lasting change unless one actively seeks to fill their life with God's presence. He cautions that neglecting spiritual vigilance can invite even greater evils into one's life, resulting in a dangerous cycle of sin and despair. The sermon serves as a call to action for believers to remain steadfast and proactive in their faith.