Albert Barnes Commentary Psalms 90:8

"Thou hast set our iniquities before thee, Our secret sins in the light of thy countenance." — Psalms 90:8 (ASV)

You have set our iniquities before you - You have arrayed them, or brought them forth to view, as a “reason” in your mind for cutting us down.

Death may be regarded as proof that God has brought before his mind the evidence of humanity’s guilt and has passed sentence accordingly.

The fact of death at all; the fact that anyone of the human race dies; the fact that human life has been made so brief—this 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 hearts. 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 your countenance - This means directly before you, in full view, so that you can see them all. In accordance with these, you judge humankind, and hence their death.