Psalms 51:6

“Behold, thou desirest truth in the inward parts, etc.] With delight and pleasure, as the word f680 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;…”

“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; Psa 119:30).”

“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…”

“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. Psalms 51:7”

“Behold: Psa 26:2, Psa 125:4; Gen 20:5, Gen 20:6; Kg2 20:3; Ch1 29:17; Ch2 31:20, Ch2 31:21; Pro 2:21; Jer 5:3; Joh 4:23, Joh 4:24; Co2 1:12; Jam 4:8 inward: Psa 5:9; Sa1 16:7; Job 38:36; Luk 11:39; Rom 7:22 in the hidden: Job 32:8; Jer 31:33, Jer 32:40; Pe1 3:4 Psalms 51:7”