III. What comfort he had in appealing to God concerning his own integrity (v. 3): But thou, O Lord! knowest me. Probably the wicked men he complains of were forward to reproach and censure him (ch. xviii. 18), in reference to which this was his comfort, that God was a witness of his integrity. God knew he was not such a one as they were (who had God near in their mouths, but far from their reins), nor such a one as they took him to be, and represented him, a deceiver and a false prophet; those that thus abused him did not know him, 1 Cor. ii. 8. "But thou, O Lord! knowest me, though they think me not worth their notice." 1. Observe what the matter is concerning which he appeals to God: Thou knowest my heart towards thee. Note, We are as our hearts are, and our hearts are good or bad according as they are, or are not, towards God; and this is that therefore concerning which we should examine ourselves, that we may approve ourselves to God. 2. The cognizance to which he appeals: "Thou knowest me better than I know myself, not by hearsay or report, for thou hast seen me, not with a transient glance, but thou hast tried my heart." God's knowledge of us is as clear and exact and certain as if he had made the most strict scrutiny. Note, The God with whom we have to do perfectly knows how our hearts are towards him. He knows both the guile of the hypocrite and the sincerity of the upright.