Charles H. Spurgeon on Psalms 104:29

Thou hidest thy face, they are troubled. So dependent are all living things upon God's smile, that a frown fills them with terror, as though convulsed with anguish. This is so in the natural world, and certainly not less so in the spiritual: saints when the Lord hides his face are in terrible perplexity. Thou takest away their breath, they die, and return to their dust. The breath appears to be a trifling matter, and the air an impalpable substance of but small importance, yet, once withdrawn, the body loses all vitality, and crumbles back to the earth from which it was originally taken. All animals come under this law, and even the dwellers in the sea are not exempt from it. Thus dependent is all nature upon the will of the Eternal. Note here that death is caused by the act of God, "thou takest away their breath"; we are immortal till he bids us die, and so are even the little sparrows, who fall not to the ground without our Father.