David Wilkerson warns about the grave danger of unbelief, using the example of the Israelites who, due to their lack of faith, were denied entry into God's rest and condemned to wander in the wilderness. He emphasizes that unbelief leads to a life consumed by personal troubles, devoid of God's presence, vision, and care for others. Wilkerson highlights that without faith, it is impossible to please God, and he reflects on the tragic fate of the unbelieving generation that wasted their lives in the wilderness. He calls Christians to recognize the peril of complacency and hardened hearts, urging them to believe in God's Word and seek spiritual growth rather than merely existing. The sermon serves as a stark reminder of the consequences of unbelief and the importance of maintaining faith in God.