[Avodah] question on the Mei Shiloach

[Ben Waxman]

In parshat Behar, the Mei Shiloach writes that we learn from Shabbat 
(the small oat (sign)) that God is the "poel" of everything and that 
nothing will come of the actions of people. Shmitta (the large oat) 
teaches us there is no power besides God.

When he says that nothing will come out of the actions of people, what 
does he mean by that?  Would anyone disagree?

Ben