Thomas Brooks emphasizes that conscience serves as God's preacher within us, acting as a witness to our actions and intentions. He warns that tampering with sin leads to a guilty conscience, which obstructs our peace and assurance in God. Brooks explains that harboring unconfessed sins creates a barrier between us and God, preventing Him from revealing His love and grace. He stresses that God will not listen to the prayers of those who continue to indulge in sin, as it is contrary to His holiness. Ultimately, a clear conscience is essential for true communion with God.