For thou hast possessed my reins,.... His thoughts and counsels, the reins being the seat of instruction and counsel; hence God is called the trier of the reins, and searcher of the hearts of the children of men; he is the possessor or master of their most secret thoughts, and thoroughly knows them; see Psa 7:9; they are also the seat of the affections, which are naturally sinful and inordinate, and set upon carnal and earthly things; but the Lord possesses and engrosses the affections of his people in the best sense, Psa 73:25; moreover the reins are the seat of lust, the bed in which it is conceived and brought forth, and God knows the first motions of it there; and that the imagination of the thought of man's heart is evil continually, Gen 6:5; thou hast covered me in my mother's womb; with the secundine, or afterbirth, in which he carefully wrapped him, a proof of his knowledge of him, and care for him in the womb; or with skin and flesh he covered his bones with as they grew there; see Job 10:11; or the sense is, he protected and defended him in his embryo state, and when ripe for birth took him out from thence, and held him up ever since, Psa 22:9; he had his eye on him when no other eye could see him, not even his mother that bare him, and before ever he himself saw light. The Targum is, "thou hast founded me in my mother's womb.''