John Calvin Commentary 1 John 3:20

"because if our heart condemn us, God is greater than our heart, and knoweth all things." — 1 John 3:20 (ASV)

For if our heart condemn us. He proves, on the other hand, that those who do not have the testimony of a good conscience possess the name and appearance of Christians in vain. For if anyone is conscious of guilt and is condemned by his own heart, he can much less escape the judgment of God. It therefore follows that faith is subverted by the disquiet of an evil conscience.

He says that God is greater than our heart, with reference to judgment; that is, because He sees much more keenly than we do, searches more minutely, and judges more severely. For this reason, Paul says that though he was not conscious of any wrong himself, yet he was not therefore justified (1 Corinthians 4:4); for he knew that however carefully attentive he was to his office, he erred in many things and through inadvertence was ignorant of mistakes which God perceived. What the Apostle means then is that whoever is harassed and condemned by his own conscience cannot escape the judgment of God.

To the same purpose is what immediately follows, that God knows or sees all things. For how can those things be hidden from Him which we, who in comparison with Him are dull and blind, are constrained to see? So, understand this explanation: “Since God sees all things, He is far superior to our hearts.” For it is not unusual to interpret a connective particle as one indicating cause. The meaning is now clear: since the knowledge of God penetrates deeper than the perceptions of our conscience, no one can stand before Him unless the integrity of his conscience sustains him.

But here a question may be raised. It is certain that the reprobate are sometimes sunk by Satan into such a stupor that they are no longer conscious of their own evils and, without alarm or fear, as Paul says, rush headlong into perdition. It is also certain that hypocrites usually flatter themselves and proudly disregard the judgment of God, for, being intoxicated by a false notion of their own righteousness, they feel no convictions of sin.

The answer to these things is not difficult: hypocrites are deceived because they shun the light, and the reprobate feel nothing because they have departed from God. Indeed, there is no security for an evil conscience except in hiding places.

But the Apostle speaks here of consciences that God draws forth to the light, forces to His tribunal, and fills with an apprehension of His judgment. Yet, it is also generally true that we cannot have calm peace except for that which God’s Spirit gives to purified hearts; for those who, as we have said, are stupefied, often feel secret compunctions and torment themselves in their lethargy.