The sermon identifies apathy, neglect of Scripture, and doubt as the primary fruits of unbelief that harden the Christian heart. It warns against spiritual blindness and indifference to evangelism, urging believers to prioritize daily engagement with God's Word as essential spiritual sustenance. The preacher emphasizes that faith is cultivated through hearing the Word and encourages a return to sincere, unwavering trust in biblical truths despite worldly distractions or rejection. By renewing the mind and rejecting double-mindedness, Christians can overcome these spiritual deficits and live with genuine purpose and holiness.