Thomas Brooks emphasizes the transformative power of gospel-obedience, which leads to a profound change in a person's character and actions. He explains that true obedience, rooted in saving faith, alters individuals from sin to sanctity and from pride to humility, aligning them with God's holy will. Brooks warns that those who have not experienced this saving change remain trapped in sin and bitterness, highlighting the necessity of genuine transformation in the life of a believer.