Thomas Brooks emphasizes that a sincere willingness to part with every sin is a clear indication of saving grace. He asserts that true integrity and saving faith are demonstrated by a person's commitment to forsake all sins, including their 'darling' sins. Brooks explains that it requires divine power and grace to overcome these beloved sins, and that a godly person does not engage in a habitual or willful practice of sin. The assurance of being upright before God is rooted in the active choice to keep oneself from sin. Ultimately, the sermon calls believers to reflect on their relationship with sin and their commitment to holiness.