If I shall say, etc. David represents himself as a man using every possible method to make his escape from a situation of embarrassment. So having acknowledged that it was vain to dream of flight, he bethinks himself of another remedy, and says, If no speed of mine can bear me out of the range of God's vision, yet, on the supposition of light being removed, the darkness might cover me, that I might have a short breath of respite. But this also he declares to be hopeless, as God sees equally well in the deepest darkness as at noon-day. 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 manifest before the eye of God. David is rather to be considered as in both clauses expressing what he might be supposed to feel desirous of, and intimates that, could he only find any covert or subterfuge, he would avail himself of the license; "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 to the robbers or wild beasts of the forest, who then range at greater liberty. That this is the proper construction of the words we may infer from the particle gm, gam. If any one should think it a very unnecessary observation to say that as respects God there is no difference between light and darkness, it is enough to remind him that all observation proves with what reluctance and extreme difficulty men are brought to come forward openly and unreservedly into God's presence. In words we all grant that God is omniscient; meanwhile what none would ever think of controverting we secretly make no account of whatsoever, in so far as we make no scruple of mocking God, and lack even that reverence of him which we extend to one of our fellow-creatures. We are ashamed to let men know and witness our delinquencies; but we are as indifferent to what God may think of us, as if our sins were covered and veiled from his inspection. This infatuation if not sharply reproved will soon change light, so far as we are concerned, into darkness, and therefore David insists upon the subject at length in order to refute our false apprehensions. Be it our concern to apply the reproofs given, and stir ourselves up by them, when we feel disposed to become secure.

If I say, Surely the darkness shall cover me - If I seek to find refuge in the darkness of the night so that God would not see me. The word rendered "cover" - שׁוף shûph - means properly to snap, to gape after; then, to lie in wait for; and then, to attack, or fall upon anyone, unexpectedly. It is rendered "bruise" (twice) in Genesis 3:15, "He shall "bruise" thy head, and thou shalt "bruise" his heel;" "breaketh" in Job 9:17, "He "breaketh" me with a tempest;" and in this place "cover." It does not occur elsewhere. Here it means to fall upon; to overpower; to cover. The idea is, If it should come suddenly upon me; if I should be involved in sudden darkness - "as if" the darkness should come and attempt to "snatch" me away from God. All this would be in vain, for it would be, so far as God is concerned, bright day around me.
Even the night shall be light about me - In respect to me. It shall be as if I stood in the full blaze of light. God can see me still; he can mark my goings; he can perceive all that I do as plainly then as at mid-day. This "is" so: and what a thought this is for a wicked man who seeks to escape detection in his crimes by perpetrating them in the night! What a thought for a good man, that in the darkest night of sorrow, when there seems to be nothing but deep midnight, when there appears to be not a ray of light in his dwelling, or on his path that all to the eye of God is as clear as noon-day! For in that night of sorrow God sees him as plainly as in the brightest days of prosperity and joy.

Surely the darkness shall cover me - Should I suppose that this would serve to screen me, immediately this darkness is turned into light.

If I say, Surely the darkness shall cover me; even the night shall be (g) light about me.
(g) Though darkness is a hinderance to man's sight, yet is serves your eyes as well as the light.

If I say, surely the darkness shall cover me,.... The darkness of a cloud or of the night, so that my actions shall not be seen; that is, if I entertain such a thought in my mind, that what I do in the dark will escape the sight and knowledge of God, and so be emboldened to commit it;
even the night shall be light about me; and make all my works manifest, as light does.