What is the meaning of "Im Yisaser Ish"?
Rashi: This is the second half of the rhetorical question "Am I G-d only over what is close [to Me]?" This is like all doubled questions said in astonishment.
Why would one think that someone can hide from Hashem?
Mesilas Yesharim (Perek 25): One might have thought that some matters are too great or too trifling for Hashem to supervise them. Rather, He sees and understands great and small, honored and lowly, without distinction.
Malbim: He would think that the distance or a barrier divides.
How does Hashem fill Shamayim and Aretz?
Radak: This is like "u'Chevod Hashem Malei Es ha'Mishkan" (Shemos 40:34). He fills the Mishkan. This was said about the created light. I fill, i.e. I am everywhere. This is a metaphor, for Hashem is not physical; He cannot fill a place! Rather, His Hashgachah is everywhere, in Shamayim and Aretz.
Radak citing Targum Yonasan: His honor fills them.
Malbim: My honor and Hashgachah fill them; nothing is hidden from Me.
