Behold, thou desirest truth in the inward parts - The word rendered "desirest," means to have pleasure in; to delight in; and the idea is that this only is agreeable to God, or this only accords with his own nature. The word rendered "inward parts," means properly the reins, and is usually employed to denote the seat of the mind, the feelings, the intellect. Compare the notes at Job 38:36. The allusion is to the "soul;" and the idea is, that God could be satisfied with nothing "but" purity in the soul. The "connection" is this: David was deeply conscious of his own pollution; his deep, early, native depravity. This, in his own mind, he contrasted strongly with the nature of God, and with what God must require, and be pleased with. He "felt" that God could not approve of or love such a heart as his, so vile, so polluted, so corrupt; and he felt that it was necessary that he should have a pure heart in order to meet with the favor of a God so holy. But how was that to be obtained? His mind at once adverted to the fact that it could come only from God; and hence, the psalm now turns from confession to prayer. The psalmist pleads earnestly Psalm 51:7-10 that God "would" thus cleanse and purify his soul.

And in the hidden part - In the secret part; the heart; the depths of the soul. The cleansing was to begin in that which was hidden from the eye of man; in the soul itself. Wisdom, heavenly, saving wisdom, was to have its seat there; the cleansing needed was not any mere outward purification, it was the purification of the soul itself.

Thou shalt make me to know wisdom - Thou only canst enable me to understand what is truly wise. This wisdom, this cleansing, this knowledge of the way in which a guilty man can be restored to favor, can be imparted only by thee; and "thou wilt do it." There is here, therefore, at the same time a recognition of the truth that this "must" come from God, and an act of faith, or a strong assurance that he "would" impart this.

Behold, thou desirest truth - I am the very reverse of what I should be. Those desirest truth in the heart, but in me there is nothing but sin and falsity.

Thou shalt make one to know wisdom - Thou wilt teach me to restrain every inordinate propensity, and to act according to the dictates of sound wisdom, the rest of my life.

Behold, thou desirest truth in the inward parts,.... With delight and pleasure, as the word (d) signifies: meaning either Christ, the truth and the life, formed and dwelling in the hearts of his people; or the Gospel, the word of truth, which has a place there; and particularly that branch of it which proclaims pardon to sensible sinners, and is the ground of hope within them: or else a true and hearty confession of sin, which David now made; or rather internal holiness and purity of heart, in opposition to the corruption of nature before acknowledged: this is what is agreeable to the nature of God, is required by his holy law, and is wrought in the hearts of his people in regeneration; and this is "truth", real, and not imaginary, genuine and unfeigned; where it is there is a true sense of sin, a right sight of Christ, unfeigned faith in him, sincere love to him, hope in him without hypocrisy, and a reverential fear of God upon the heart; the inward parts are the seat of all this, and in the exercise of it the Lord takes great delight and pleasure;

and in the hidden part thou shall make me to know wisdom; either Christ, the wisdom of God; or the Gospel, and particularly that part of it which concerns the pardon of sin; or a true knowledge of sin, and of the way of life and salvation by Christ, which is the truest and highest wisdom: and the phrase "hidden" or "secret" may either denote the nature of the wisdom made known, which is hidden wisdom, the wisdom of God in a mystery; or the manner in which it is made known; it is in a hidden way, privately, and secretly, and indiscernibly like the wind, by the Spirit and grace of God; or the seat and subject of it, "the hidden part", as we supply it; the hidden man of the heart. David begins to rise in the exercise of his faith in the grace of God, "thou shall make me to know", &c. unless the words should be rendered as a prayer, as they are by some, "make me to know" (e), &c. and as are the following.

(d) "delectaris", Junius & Tremellius, Piscator; "delectatus es", Cocceius; so Ainsworth. (e) "notam mihi fac", Gejerus.

Behold, thou {f} desirest truth in the inward parts: and in the hidden part thou shalt make me to know wisdom.

(f) He confesses that God who loves pureness of heart, may justly destroy man, who by nature is a sinner much more him whom he had instructed in his heavenly wisdom.

51:6 Truth - Uprightness of heart; and this may be added; as an aggravation of the sinfulness of original corruption, because it is contrary to the holy nature and will of God, which requires rectitude of heart: and, as an aggravation of his actual sin, that it was committed against that knowledge, which God had wrote in his heart.

6. thou shalt make, &c.-may be taken to express God's gracious purpose in view of His strict requisition; a purpose of which David might have availed himself as a check to his native love for sin, and, in not doing so, aggravated his guilt.

truth . and .wisdom-are terms often used for piety (compare Job 28:28; Ps 119:30).

51:1-6 David, being convinced of his sin, poured out his soul to God in prayer for mercy and grace. Whither should backsliding children return, but to the Lord their God, who alone can heal them? he drew up, by Divine teaching, an account of the workings of his heart toward God. Those that truly repent of their sins, will not be ashamed to own their repentance. Also, he instructs others what to do, and what to say. David had not only done much, but suffered much in the cause of God; yet he flees to God's infinite mercy, and depends upon that alone for pardon and peace. He begs the pardon of sin. The blood of Christ, sprinkled upon the conscience, blots out the transgression, and, having reconciled us to God, reconciles us to ourselves. The believer longs to have the whole debt of his sins blotted out, and every stain cleansed; he would be thoroughly washed from all his sins; but the hypocrite always has some secret reserve, and would have some favorite lust spared. David had such a deep sense of his sin, that he was continually thinking of it, with sorrow and shame. His sin was committed against God, whose truth we deny by wilful sin; with him we deal deceitfully. And the truly penitent will ever trace back the streams of actual sin to the fountain of original depravity. He confesses his original corruption. This is that foolishness which is bound in the heart of a child, that proneness to evil, and that backwardness to good, which is the burden of the regenerate, and the ruin of the unregenerate. He is encouraged, in his repentance, to hope that God would graciously accept him. Thou desirest truth in the inward part; to this God looks, in a returning sinner. Where there is truth, God will give wisdom. Those who sincerely endeavour to do their duty shall be taught their duty; but they will expect good only from Divine grace overcoming their corrupt nature.