Thomas Brooks emphasizes the danger of relying on our good works for salvation, warning that while duties are important, they can lead to pride and self-reliance. He cites the wisdom of Luther, urging believers to be cautious not only of their sins but also of their good deeds, which can become a false source of security. Brooks argues that trusting in one's own righteousness is as perilous as open wickedness, leading to spiritual ruin. He calls for a complete renunciation of self-righteousness and a reliance solely on the righteousness of Jesus Christ and the grace of God.

It was the saying of a precious saint—that he was more afraid of his duties than of his sins; for his duties often made him proud—but his sins always made him humble. It was good counsel Luther gave, "We must take heed not only of our sins—but of our good works." Duties can never have too much diligence used about them—nor too little confidence placed in them. They are good helps—but bad saviors. It is necessary we do them —but it is dangerous to rely upon them. If the devil cannot dissuade us from performing pious duties—then his next work will be to persuade us to rely upon them, to make saviors of them; because this will as certainly ruin our souls, as if we had wholly neglected them. Resting in your own righteousness, will as certainly and eternally undo you—as the greatest and foulest atrocities! Open wickedness slays her thousands—but a secret resting upon duties, slays her ten thousands! Open profaneness is the broad dirty way which leads to hell; but trusting in pious duties is as sure a way, though a cleaner way to hell. Ungodly people and formal professors shall meet at last in the same hell. Now, let all these things work you to renounce your own righteousness—and to take sanctuary alone in the pure, perfect, and most glorious righteousness of Jesus Christ, and in the free grace of God.