Prove me, [1] O Jehovah! The more that David observed himself basely and undeservedly pursued with calumnies, the more powerfully was he excited by the vehemence of his grief fearlessly to assert his rectitude. Nor does he merely clear himself of outward sins; he glories also in the uprightness of his heart, and the purity of its affections, tacitly comparing himself, at the same time, with his enemies. As they were gross hypocrites, proudly boasting of their reverence for God, he lays open before him their shameless effrontery and hardihood. This protestation, too, shows how intimately acquainted he was with himself, when he durst offer to submit the whole recesses of his heart to the examination of God. It is to be observed, however, that it was the wickedness of his enemies which forced him to commend himself so much. Had he not been unjustly condemned by men, he would have humbly deprecated such an examination, as he well knew, notwithstanding his zeal to act aright, that he was far from perfection. But when he felt himself to be falsely accused, the injustice and cruelty of men emboldened him to appeal to God's judgment-seat without hesitation. And as he knew that an external appearance of innocence was of no avail there, he brings forward the honest uprightness of his heart. The distinction which some make here, that the heart signifies the higher affections, and the reins those that are sensual (as they term them) and more gross, is more subtle than solid. We know that the Hebrews understood by the term reins that which is most secret in men. David, therefore, conscious of his innocence, offers the whole man to the examination of God; not like careless, or rather stupid men, who, flattering themselves, imagine that they will deceive God with their pretences. It is evident, on the contrary, that he had honestly and thoroughly searched himself, before he presented himself with such confidence in the divine presence. And this we must especially bear in mind, if we would desire to obtain the approbation of God, that when unjustly persecuted, we must not only abstain from retaliation, but also persevere in a right spirit.

Footnotes

1 - The primary signification of the Hebrew word tsrph, tsaraph is to try as the refiner tries his gold by dissolving and melting it, In this sense it is used in Psalm 66:10, "Thou hast tried us as silver is tried."

Examine me, O Lord - The meaning of this verse is, that he asked of God a strict and rigid examination of his case. To express this, the psalmist uses three words - "examine; prove; try." These words are designed to include the modes in which the reality of anything is tested, and they imply together that he wished the most "thorough" investigation to be made; he did not shrink from any test. He evidently felt that it was essential to his welfare that the most rigid examination should be made; that the exact truth should be known; that if he was deceived, it was best for himself that he should not be left under the delusion, but that, understanding his own case, he might be led to secure his salvation. The word rendered "examine" means, "to try, to prove," and is applicable especially to metals: Jeremiah 9:7; Zac 13:9. It means here, "Apply to me such tests as are applied to metals in order to determine their genuineness and their value."
And prove me - A word of similar import. In the original meaning of the word there is a reference to "smell;" to try by the smell; to ascertain the qualities of an object by the smell. Hence, it comes to be used in a more general sense to denote any way of ascertaining the quality of an object.
Try my reins - The word here rendered "try" (test) is one that is most commonly applied to metals; and the three words together express the earnest desire of the psalmist that God would examine into the evidences of his piety - those evidences to which he immediately refers - and apply the proper kind of tests to determine whether that piety was genuine. The word rendered "reins" means properly the "kidneys," and hence, it is used to denote the inward part, the mind, the soul - the seat of the desires and the affections. See Psalm 7:9, note; Psalm 16:7, note. We speak now of the "heart" as the seat of the affections or of love. The Hebrews more commonly spoke of the heart as the seat of intelligence or knowledge, and the reins or the "bowels" as the seat of the affections. In itself there was no more impropriety in their speaking of the reins or kidneys as the seat of the affections than there is of our speaking of the heart in that manner. Neither of them is strictly correct; and both modes of speech are founded on popular usage.

Examine me, O Lord - To thee I appeal; and feel no hesitation in wishing to have all the motives of my heart dissected and exposed to thy view, and to that of the world.

Examine me, O LORD, and prove me; try my (b) reins and my heart.
(b) My very affections and inward motions of the heart.

Examine me, O Lord,.... His cause, his integrity, and trust in the Lord, as silver and gold are examined by the touchstone, the word of God, which is the standard of faith and practice;
and prove me; or "tempt me" (r); as Abraham was tempted by the Lord; and his faith in him, and fear of him, and love to him, were proved to be true and genuine;
try my reins and my heart; the thoughts, desires, and affections of it, as gold and silver are tried in the furnace; and so God sometimes tries the faith and patience of his people by afflictive providences; and this examination, probation, and trial, are made by him, not for his own sake, who knows the hearts and ways of all men; but for the sake of others, to make known either to themselves or others the truth of grace that is in them, and the uprightness of their hearts and ways; and it was on this account the psalmist desired to pass under such an examination.
(r) "tenta me", Pagninus, Montanus, Junius & Tremellius, &c.

He asks the most careful scrutiny of his affections and thoughts (Psalm 7:9), or motives.