Why does it say "Kol Ma'asav"?
Rashi: They are in all places of His sovereignty.
Radak: This refers to lower beings. All are His deeds, and His sovereignty is over all of them. They are the four 'elements' and all that is made from them - living beings, vegetation and inanimate, e.g. rocks, earth and metals.
Malbim: This refers to creations of the lower world, which is the final deed.
Why does it say "b'Chol Mekomos Memshalto"?
Radak: They were created below in different places - some on the land, some in the seas, and some in the air.
Malbim: His sovereignty reaches also to this lower world, whether via angels that conduct wondrously, or via natural conduct of the Ma'arachah.
Why does it repeat "Barchi Nafshi Es Hashem"?
Brachos 10a: David left the womb, saw stars and constellations ("Barchu Hashem Mal'achav" - verse 20), and said Shirah.
Radak: He is above all lower beings, and man, with his intellect, rules over them - "Tamshilehu b'Ma'ase Yadecha" (8:7). The [other] lower beings have no Da'as to bless and praise. Rather, man blesses Kel for them - for their creation and their deeds. It is as if they bless. Also "Oh Si'ach la'Aretz v'Soreka vi'Ysapru Lecha Degei ha'Yam" (Iyov 12:8) is like this. Therefore, the Mizmor begins and ends with Barchi Nafshi, for man, with his supreme Nefesh, encompasses everything with his Chachmah, and understands upper and lower beings; he should bless Hashem for everything.
Malbim: The Nefesh encompasses all worlds. The body is like nature of the lower worlds with fixed laws. The Nefesh itself is like the world of angels to override nature itself and heed His word. Hashem grafted into the Nefesh all acts of Bereishis and all worlds, so it blesses Hashem corresponding to all of them.
