John Calvin Commentary Psalms 139:13

"For thou didst form my inward parts: Thou didst cover me in my mother`s womb." — Psalms 139:13 (ASV)

For you have possessed my reins. Apparently, the psalmist pursues the same subject, though he carries it out somewhat further. He declares that we need not be surprised at God’s knowledge of the most secret thoughts of people, since He formed their hearts and their reins.

The psalmist thus represents God as enthroned in the very reins of humanity, as the center of His jurisdiction. This shows it should be no cause for wonder that all the windings and recesses of our hearts are known to Him. After all, when we were enclosed in our mother’s womb, He saw us as clearly and perfectly as if we had stood before Him in the light of midday.

This helps us understand the purpose with which David proceeds to speak of humanity’s original formation. Its scope is the same in the verse that follows. There, despite some ambiguity in the terms used, it is sufficiently clear and obvious that David means he had been fashioned in a wonderful manner, calculated to inspire both awe and admiration, so that he bursts forth into praises of God.

One great reason for the carnal security into which we fall is our failure to consider how uniquely we were fashioned at first by our Divine Maker. From this particular instance, David is led to refer generally to all the works of God, which are just so many wonders designed to draw our attention to Him.

The true and proper view to take of God’s works, as I have observed elsewhere, is that which ends in wonder. His declaration that his soul should well know these wonders, which far transcend human comprehension, simply means that with humble and sober application, he would direct his attention and abilities toward gaining such an understanding of God’s wonderful works as might lead to adoring the immensity of His glory.

The knowledge he means, therefore, is not one that professes to comprehend what, under the name of wonders, he admits to be incomprehensible. Nor is it the kind that philosophers presumptuously claim, as if they could solve every mystery of God. Rather, it is simply that religious attention to God’s works which inspires the duty of thanksgiving.