Verse 20. - Our heart means our conscience, not the affections, which would be σπάγχνα (verse 17). If we are conscious of sincere and habitual love, this will calm us when conscience reproaches us (comp. 1 John 1:9; 1 John 2:1, 2). St. John never uses the more technical term συνείδησις, which occurs in the Acts and 1 Peter, and is very frequent in St. Paul. God is greater than our heart. It is asked whether this means that he is more merciful or more rigorous. Neither the one nor the other. It means that, although our conscience is not infallible, God is. Our hearts may be deceived; he cannot be. He knoweth all things. An awful thought for the impenitent, a blessed and encouraging thought for the penitent, He knows our sins; but he also knows our temptations, our struggles, our sorrow, and our love.

3:16-21 Here is the condescension, the miracle, the mystery of Divine love, that God would redeem the church with his own blood. Surely we should love those whom God has loved, and so loved. The Holy Spirit, grieved at selfishness, will leave the selfish heart without comfort, and full of darkness and terror. By what can it be known that a man has a true sense of the love of Christ for perishing sinners, or that the love of God has been planted in his heart by the Holy Spirit, if the love of the world and its good overcomes the feelings of compassion to a perishing brother? Every instance of this selfishness must weaken the evidences of a man's conversion; when habitual and allowed, it must decide against him. If conscience condemn us in known sin, or the neglect of known duty, God does so too. Let conscience therefore be well-informed, be heard, and diligently attended to.For if our heart condemn us,.... Of want of love to the brethren, and of hypocrisy in it, as well as of any other sin; for the conscience, which is meant by the heart here, is accuser, witness and judge; it accuses of the evil of sin, and is as good as a thousand witnesses; and upon its own testimony pronounces guilty, and condemns.

God is greater than our heart: for he is the Maker of it, and he has the power over it, and the management of it; it is in his hands, and to be turned by him as he pleases; and he is the searcher and trier of it; and besides, is a swifter witness than conscience, and a superior Judge unto it.

And knoweth all things; that are in the heart; the principles of actions, and all the actions of men, for which their hearts condemn them; and all the sinfulness in them, and the aggravations of them; wherefore, as he knows them more perfectly, he judges of them more exactly, and will reprove more sharply, and condemn more severely for them: hence, if the condemnation of men's hearts and consciences be so very great, as sometimes to be intolerable and insupportable, what will be the righteous judgment, and dreadful condemnation of God? how fearful a thing will it be to fall into the hands of the living God! this sense is confirmed by the Syriac version rendering it, "how much greater is God than our hearts?" there is another sense given by some, which is not by way of terror, but comfort, and that is, that if the hearts of believers accuse, reprove, and condemn for sin through unbelief, or want of clear view of pardon and righteousness by Christ, God is greater, as in power, so in knowledge, than the hearts of men; and he knows the thoughts he has towards them, which are of peace, and not of evil; the covenant he has made with his Son, of which he is ever mindful; and what his Son has done, that he has made full satisfaction for sin, and brought in an everlasting righteousness: so that let sin, or Satan, or the world, or the law, or their own hearts condemn them, there is no condemnation of any avail unto them. But the former sense seems best to agree with the context.