John Calvin Commentary Psalms 139:11

"If I say, Surely the darkness shall overwhelm me, And the light about me shall be night;" — Psalms 139:11 (ASV)

If I shall say, etc. David represents himself as a man using every possible method to escape from an embarrassing situation. So, having acknowledged that it was futile to dream of flight, he considers another remedy and says, If no speed of mine can take me beyond the range of God’s vision, yet, if light were removed, the darkness might cover me, so that I might have a brief moment of relief.

But this also he declares to be hopeless, as God sees equally well in the deepest darkness as at midday. It is a mistake, in my opinion, to consider, as some have done, that the two clauses of the verse are to be taken separately and read, If I shall say the darkness will cover me, even the night shall be as light before me—meaning that darkness would be converted into light, and so, though he saw nothing himself, he would stand revealed before God’s eyes.

David is rather to be considered as expressing in both clauses what he might be supposed to be wishing for, and intimates that, if he could only find any cover or subterfuge, he would take advantage of the opportunity: “If I shall say, at least the darkness will cover me, and the night be as light for me”—that is, in the sense in which it is so for robbers or wild beasts of the forest, who then roam more freely.

We may infer that this is the proper interpretation of the words from the particle גם, gam.

If anyone should think it a very unnecessary observation to say that, regarding God, there is no difference between light and darkness, it is enough to remind him of a truth confirmed by all observation: people are brought to come forward openly and unreservedly into God’s presence only with great reluctance and extreme difficulty.

In words, we all grant that God is omniscient. However, we secretly disregard this truth—a truth no one would openly dispute—to the point that we do not hesitate to mock God. Indeed, we often lack even the basic reverence for Him that we would show to our fellow human beings.

We are ashamed to let others know and witness our wrongdoings. Yet, we are as indifferent to what God may think of us as if our sins were covered and hidden from His sight.

If this delusion is not sharply corrected, it will soon, for us, turn light into darkness. Therefore, David discusses this subject at length to refute our false understandings.

Let us then make it our concern to apply these rebukes and rouse ourselves with them whenever we feel inclined to become complacent.