1 John 3:20

For if our heart condemn us - We cannot hope for peace from any expectation that our own hearts will never accuse us, or that we ourselves can approve of all that we have done. The reference here is not so much to our past lives, as to our present conduct and deportment. The object is to induce Christians so to live that their hearts will not condemn them for any secret sins, while the outward deportment may be unsullied. The general sentiment is, that if they should so live that their own hearts would condemn them for present insincerity and hypocrisy, they could have no hope of peace, for God knows all that is in the heart. In view of the past - when the heart accuses us of what we have done - we may find peace by such evidences of piety as shall allay the troubles of an agitated soul, 1 John 3:9, but we cannot have such peace if our hearts condemn us for the indulgence of secret sins, now that we profess to be Christians. If our hearts condemn us for present insincerity, and for secret sins, we can never “persuade” or soothe them by any external act of piety. In view of the consciousness of past guilt, we may find peace; we can find none if there is a present purpose to indulge in sin.

God is greater than our heart, and knoweth all things - We cannot hope to find peace by hiding anything from his view, or by any supposition that he is not acquainted with the sins for which our consciences trouble us. He knows all the sins of which we are conscious, and sees all their guilt and aggravation as clearly as we do. He knows more than this. He knows all the sins which we have forgotten; all those acts which we endeavor to persuade ourselves are not sinful, but which are evil in his sight; and all those aggravations attending our sins which it is impossible for us fully and distinctly to conceive. He is more disposed to condemn sin than we are; he looks on it with less allowance than we do. We cannot hope, then, for a calm mind in any supposition that God does not see our sins as clearly as we do, or in any hope that he will look on them with more favor and indulgence. Peace cannot be found in the indulgence of sin in the hope that God will not perceive or regard it, for we can sooner deceive ourselves than we can him; and while therefore, 1 John 3:19, in reference to the past, we can only “persuade” our hearts, or soothe their agitated feelings by evidence that we are of the truth now, and that our sins are forgiven; in reference to the present and the future, the heart can be kept calm only by such a course of life that our own hearts and our God shall approve the manner in which we live.