Thou hast set our iniquities before thee. To show that by this complaint he is far from intending to murmur against God, he asserts that the Divine anger, however terrible it had been, was just, inasmuch as the people had provoked it by their iniquities; for those who, when stricken by the Divine hand, are not brought to genuine humiliation, harden themselves more and more. The true way to profit, and also to subdue our pride, is to feel that He is a righteous judge. Accordingly Moses, after having briefly taught that men by nature vanish away like smoke, gathers from thence that it is not to be wondered at if God exanimates and consumes those whom he pursues with his wrath. The manner of the expression by which God is described as showing the tokens of his anger is to be observed -- he sets the iniquities of men before his eyes Hence it follows, that whatever intermission of punishment we experience ought in justice to be ascribed to the forbearance of. God, who buries our sins that he may spare us. The word lvmym, alumim, which I have rendered our secret sins, is translated by some, our youth; [1] as if Moses had said that the faults committed in youth are brought to remembrance. But this is too forced, and inconsistent with the scope of the passage; for it would destroy the contrast between secret sins and the light of God's countenance, by which Moses intimates that men hide themselves in darkness, and wrap themselves in many deceits, so long as God does not shine upon them with the light of his judgment; whereas, when he draws them back from their subterfuges, by which they endeavor to escape from him, and sets before his eyes the sins which they hide by hypocrisy, being subdued by fear and dread, they are brought sincerely to humble themselves before him.

Footnotes

1 - "In the Indies," says Sir John Chardin, "the parts of the night are made known, as well by instruments (of music,) in great cities, as by the rounds of the watchmen, who, with cries and small drums, give notice that a fourth part of the night is passed. Now, as these cries awaked those who had slept all that quarter part of the night, it appeared to them but as a moment." -- Harmer's Observations, volume 1, page 333. If this psalm was the production of Moses, it is observable that night watches were in use in his time.

Thou hast set our iniquities before thee - Thou hast arrayed them, or brought them forth to view, as a "reason" in thy mind for cutting us down. Death may be regarded as proof that God has brought before his mind the evidence of man's guilt, and has passed sentence accordingly. The fact of death at all; the fact that anyone of the race dies; the fact that human life has been made so brief, is to be explained on the supposition that God has arrayed before his own mind the reality of human depravity, and has adopted this as an illustration of his sense of the evil of guilt.
Our secret sins - literally, "our secret;" or, that which was concealed or unknown. This may refer to the secret or hidden things of our lives, or to what has been concealed in our own bosoms; and the meaning may be, that God has judged in the case not by external appearances, or by what is seen by the world, but by what "he" has seen in the heart, and that he deals with us according to our real character. The reference is, indeed, to sin, but sin as concealed, hidden, forgotten; the sin of the heart; the sin which we have endeavored to hide from the world; the sin which has passed away from our own recollection.
In the light of thy countenance - Directly before thee; in full view; so that thou canst see them all. In accordance with these, thou judgest man, and hence, his death.

Thou hast set our iniquities before thee - Every one of our transgressions is set before thee; noted and minuted down in thy awful register!
Our secret sins - Those committed in darkness and privacy are easily discovered by thee, being shown by the splendours of thy face shining upon them. Thus we light a candle, and bring it into a dark place to discover its contents. O, what can be hidden from the allseeing eye of God? Darkness is no darkness to him; wherever he comes there is a profusion of light - for God is light!

Thou hast set our sins before thee,.... The cause of all trouble, consumption, and death; these are before the Lord, as the evidence, according to which he as a righteous Judge proceeds; this is opposed to the pardon of sin, which is expressed by a casting it behind his back, Isaiah 38:17,
our secret sins in the light of thy countenance; the Targum and Jarchi interpret it of the sins of youth; the word is in the singular number, and may be rendered, "our secret sin" (f); which has led some to think of original sin, which is hidden from, and not taken notice of by, the greatest part of the world, though it is the source and spring of all sin. It is not unusual for the singular to be put for the plural, and may intend all such sins as are secretly committed, and not known by other men, and such as are unobserved by men themselves; as the evil thoughts of their hearts, the foolish words of their mouths, and many infirmities of life, that are not taken notice of as sins: these are all known to God, and will be brought to light and into judgment by him, and will be set in "the light of his countenance"; which denotes not a gracious forgiveness of them, but his clear and distinct knowledge of them, and what a full evidence they give against men, to their condemnation and death; and intends not only a future, but the present view the Lord has of them, and his dealings with men in life, and at death, according to them.
(f) "mostrum absconditum", Montanus; "sive occultum", Vatablus, Muis, Michaelis.

Hast set - Thou dost observe them, as a righteous judge, and art calling us to an account for them. Secret sins - Which though hid from the eyes of men, thou hast brought to light by thy judgments.