An important theme in the New Testament is the role that conscience plays in human lives. We immediately think of its role in the life of the believer, but we should never forget that the unbeliever has a conscience, too, though he deals with it in a very different way.
Let’s start with the origin of the conscience: “They [i. e., the Gentiles] show that the work of the law is written on their hearts, while their conscience also bears witness, and their conflicting thoughts accuse or even excuse them” (Romans 2:15). This verse shows that the conscience is part of the image of God, which, though marred by sin, remains in every man. It is a remnant of the Law of God which had been implanted in the heart of Adam, and which is renewed in the heart of every believer as part of regeneration (Hebrews 10:16).
That conscience in the unbeliever will always produce a reaction, but that reaction can be in either of two directions, as the verse above indicates. For the reprobate, the conscience is solely a source of accusation. We see this, for example, in Judas after the crucifixion of Jesus (Matthew 27:3). Did Judas seek forgiveness for his betrayal? No. Rather, he committed suicide (Matthew 27:5, Acts 1:18-19). These possibilities, guilt or forgiveness, are the only two possible reactions to the truth of the Gospel (II Corinthians 2:16).
For the elect, his conscience drives him to the only place that he can clear his conscience, to faith in Jesus’s atoning blood (I Peter 3:21). For the reprobate, the conscience can never be salved, but can only be suppressed (Romans 1:18).
“The burden which presses with intolerable weight upon the soul is the terrible conviction, wrung from the depths of our moral natures. that we have done wrong and deserve to die. It is this feeling that we deserve our doom which kindles the hell within us. If we would strip ourselves of the burning consciousness of this fact, no amount of evil could ever be regarded in the light of punishment.” —James Henley Thornwell, The Necessity and Nature of Christianity