The Conscience

Everyone knows the feeling. The inner voice that approves when you do right and accuses when you do wrong, the discomfort that follows a lie even when no one will ever find out, the quiet sense that some things are simply wrong in themselves. The Bible calls this the conscience, and treats it as one of the most telling pieces of evidence about what a human being is: not a clever animal running on instinct, but a moral creature, answerable to a moral God. It is also, the Bible is honest enough to say, a fragile instrument. The conscience can be trained or dulled, sharpened or hardened, healed or, most frighteningly, switched off.

The law written on the heart

Where does this inner witness come from? Paul says it is the fingerprint of God's moral law pressed into human nature itself. Even people who never received the written commandments, he says, "shew the work of the law written in their hearts, their conscience also bearing witness" (Romans 2:14-15). That is why a sense of right and wrong shows up in every culture on earth, however differently applied. The conscience is the echo in us of a law that is not our invention, which is exactly the argument C.S. Lewis pressed: a universal moral sense points beyond us, to a Lawgiver who wrote it there (see the moral argument).

The courtroom inside

Paul's picture of the conscience is a tiny trial held in the soul: our thoughts "accusing or else excusing one another" (Romans 2:15). Inside every person a small court is always in session, returning a verdict on what we have done. A clear verdict is one of life's great goods. Paul made it his aim "to have always a conscience void of offence toward God, and toward men" (Acts 24:16), and named "a good conscience" as one of the goals of the whole Christian life (1 Timothy 1:5). To live with an accusing conscience is a special kind of misery; to live with a clear one is a quiet kind of wealth.

But it is a witness, not the judge

Here honesty is vital, because the conscience is often treated as the final word, and it is not. It is a witness that reports according to how it has been taught, and it can go wrong in both directions. It can be over-tender and weak, condemning things God permits (1 Corinthians 8:7), so that a fearful believer is bound by scruples the Bible never imposed. It can be "defiled" (Titus 1:15). And most chillingly, it can be silenced altogether by repeated sin until it stops speaking, "having their conscience seared with a hot iron" (1 Timothy 4:2). So a calm conscience is not proof of innocence, as Paul knew: "I know nothing by myself; yet am I not hereby justified" (1 Corinthians 4:4). And a screaming conscience is not always the final truth either, for "if our heart condemn us, God is greater than our heart" (1 John 3:20). The conscience must be calibrated, taught by the truth of God's word, neither blindly trusted nor ignored.

You cannot scrub it clean yourself

And here is the deepest problem the conscience exposes: a genuinely guilty conscience cannot be talked out of its verdict, and we cannot wash it clean ourselves. We try. We distract it, lower the standard, blame our upbringing, stay busy, or simply sear it until it goes quiet. None of that actually cleanses it; it only muffles or kills the witness. The Bible says there is exactly one thing that truly purges a guilty conscience, and it is not self-justification but the blood of Christ, which alone can "purge your conscience from dead works to serve the living God" (Hebrews 9:14), so that we may draw near "having our hearts sprinkled from an evil conscience" (Hebrews 10:22). You can see it happen in the dust outside the temple, when Jesus answered a mob holding stones: "He that is without sin among you, let him first cast a stone at her" (John 8:7). One by one they dropped the stones and left, "convicted by their own conscience" (John 8:9). He alone could both expose the conscience and, for the woman left standing there, clear it.

Two things the early church did with it

The doctrine here is Paul's and the page rests on his sentence, not on anyone else's. But two early uses of it are worth having, because they show what the church did with the verse once it had it.

It answered a hard question about everyone before Moses. Archelaus, in the third century, puts it plainly: "whence, then, did righteous Abel and all those succeeding worthies, who are enrolled among the righteous, derive their righteousness when as yet there was no law of Moses, and when as yet the prophets had not arisen and discharged the functions of prophecy?" The law written on the heart is his answer, and it is the same answer Paul is giving about the Gentiles who "shew the work of the law written in their hearts" (Romans 2:15). A man with no Bible is not a man with no witness.

And Augustine ties the verse to another one, which sharpens both. Paul tells the Corinthians they are "written not with ink, but with the Spirit of the living God; not in tables of stone, but in fleshy tables of the heart" (2 Corinthians 3:3). Augustine says what Paul attributes to those Gentiles "must be some such thing as what he says to the Corinthians." The same finger writes in both places. The conscience of a pagan and the new covenant in a believer are not unrelated things; they are the same God writing on the same material, at different depths.

Augustine also takes it where this page has already taken it, to the end: at the judgment "the Lord shall be a swift witness, when He shall suddenly bring back into the memory that which shall convince and punish the conscience." Which is why conscience is a witness and not the judge. It testifies now, and it will testify then, and the verdict is not its own to give.

Chrysostom, reading the same passage, presses on what it would mean if the faculty were not there at all:

The argument runs backwards from the verdict. A man cannot be justly answerable for what he was never given any means of knowing, so the fact that he is answerable is itself evidence that something in him was telling him.

Augustine took the same verse forward to the day it is pointed at, and found the terrible economy in it: nothing new has to be gathered for that trial.

Where this lands

The conscience is a gift, an alarm bell God set ringing inside you so that you would not sleep through your own ruin. But it was never meant to be your savior, only your witness. Listen to it; do not sear it. Train it by the truth until it rings true. And when it convicts you, do not answer it with excuses or with despair, but carry the charge to the cross, where the blood of Christ does what no amount of self-justifying ever could: it does not pretend you are innocent, it makes you clean (see the cross and repentance).

Related: C.S. Lewis, The Cross, Repentance, and the Heart. Scripture from the King James Version, linked to BibleHub; the words of Christ are marked in purple.