Why does it say "ba'Hachinu Shamayim Sham Ani"?
Malbim: Hashem prepared the Raki'a to be called Shamayim (Bereishis 1:8) - this was via the laws of Chachmah.
What is "Chug"?
Rashi: It is an expression of surrounding, like "uva'Mechugah Yesa'arehu" (Yeshayah 44:13; he makes circles with a compass).
What is the meaning of "b'Chuko Chug Al Pnei Sehom"?
Tanchuma (Bereishis 1): Hashem used the Torah seal the Tehom, lest it flood the world. Ma'alos ha'Torah (DH Od Isa) - these Chukim are carved onto the Yetzer ha'Ra.
Rashi: When He stretched the land on the water, He made a boundary that it will not pass.
Malbim: This law that Hashem made, that the upper water will stand in the Raki'a (sky), which is like a Chug (ball) over the depth to receive water of the depth in clouds, this revealed the dry land. Via it, the water of the depths was gathered in the sea.
