For thou hast possessed my reins: thou hast covered me in my mother's womb. Thou hast possessed my reins - As the Hebrews believed that the reins were the first part of the human fetus that is formed, it may here mean, thou hast laid the foundation of my being.
Related Commentaries of Psalms 139:13
Psalms 139:13
13 For thou hast possessed my reins: thou hast covered me in my mother's womb.