Albert Barnes Commentary Psalms 104:28

"Thou givest unto them, they gather; Thou openest thy hand, they are satisfied with good." — Psalms 104:28 (ASV)

That thou givest them they gather - What you place before them they collect. They have no resources of their own. They can invent nothing; they cannot vary their food by human skill, as humans do; they cannot make use of reason, as humans do, or of skill, in preparing it to suit and pamper the appetite. It comes prepared for them directly from the hand of God.

Thou openest thine hand - As one does who bestows a gift on another. The point in the passage is that they receive it immediately from God, and that they are wholly dependent on him for it. They do not have to labor to prepare it, but it is made ready for them, and they only have to gather it up. The allusion in the language may be to the gathering of manna in the wilderness, when it was provided by God, and people had only to collect it for their use. So it is with the animal creation on land and in the waters.

They are filled with good - They are satiated with good; that is, they are satisfied with what to them is good, or with what supplies their needs.