Thomas Brooks emphasizes that conscience acts as God's spy within our hearts, serving as a personal tribunal that records our actions and thoughts. He illustrates how conscience functions as a witness, documenting every secret sin and wrongdoing, regardless of how well we try to conceal them. Brooks points out that even in the most hidden circumstances, conscience will ultimately reveal the truth and hold us accountable before God. The sermon highlights the inescapable nature of conscience, which serves as both a guide and a judge in our moral lives.

Conscience is God's spy in the heart. 'Conscience,' says Philo, 'is the little tribunal of the soul. Conscience is a thousand witnesses, for or against a man. Conscience is a court of record, and whatever it sees it writes down; and conscience is always as quick in writing as the sinner can be in sinning.' The very heathen could say that conscience was a god to every man. Conscience, as a scribe, a register—sits in the closet of your hearts, with pen in hand, and makes a journal of all your secret ways and secret crimes, which are above the cognizance of others. Conscience sets down the time when, the place where, the manner how, and the people with whom—such and such secret wickednesses have been committed; and that so clear and evident, that, go where you will, and do what you can, the characters of them shall never be cancelled or erased out, until God appears in judgment. Let a man sin in the most hidden seclusion which human policy can contrive, let him take all the ways he can to hide his sins, to cloak and cover his sin, as Adam did—yet conscience will so play the judge, that it will bring in the evidence, produce the law, urge the penalty, and pass the sentence of condemnation upon him.