In this sermon, Charles Haddon Spurgeon discusses four doctrines that provide strong consolation and protection for believers in times of doubt and attack on their faith. The first doctrine addresses the issue of unbelief, which God foresaw and countered by smiting it four times to ensure its defeat. The second doctrine acknowledges the constant attacks on believers' faith by the world, sin, and the devil, and how God has fortified them with four strong lines of protection. Spurgeon emphasizes the importance of these doctrines in fortifying believers' hearts when faced with challenges. He concludes by urging listeners to seek an interest in these precious doctrines and highlights the power and excellence of the doctrine itself.