1)
Why does it say "Tastir Panecha Yibalehun"?
1.
Radak, Malbim: When You hide Your face, i.e. withhold their food, they are confounded, for they have no ability without You; they die.
2)
What is the meaning of "Tosef Rucham"?
1.
Rashi: This is an expression of being finished off, like "Safu Tamu" (73:19).
2.
Radak: "Tosef" is like Te'esof (with an Aleph, which refers to death) - "Rucho v'Nishmaso Elav Ye'esof" (Iyov 34:14).
3.
Malbim: The Ru'ach that You breathed into them is gathered, and they die.
3)
Why does it say "v'El Afaram Yeshuvun"?
1.
Radak, Malbim: When the Ru'ach leaves the living, the body returns to earth.
