Why did he say "Rabos Asisa"?
Radak: You did for me many matters like this.
Malbim: What You did in six days of creation is great. You engraved matters in man's heart, e.g. to bring a Korban to You amidst thanks; we would know this even if it were not written in the Torah. Kayin and Hevel brought Korbanos, even though they were not commanded!
Why did he say "Nifle'osecha u'Machshevosecha Eleinu"?
Rashi: For us You created Your world, You split the sea, and You planned from afar to benefit us. You delayed us in the Midbar for 40 years due to the Emori'im who cut their trees and made their land desolate when they heard that Yisrael are coming to inherit their land 1 .
Radak: Nifle'os are at the time of the action; Machashavos are before the action. It is an anthropomorphism (to discuss Hashem thinking before He acts); Dibrah Torah k'Leshon Bnei Adam (Brachos 31b). We find like this - "Hinei Anochi
Tanchuma (Re'eh 7): Hashem promised to Yisrael a land full of good! During the 40 years, the Kena'anim despaired of Yisrael; they replanted trees and fixed the land.
What is the meaning of "Ein Aroch Elecha"?
Rashi: One cannot compare to You any officer or savior. "Aroch" is like "k'Erkecha" (Vayikra 27:12). Radak - "Mi va'Shachak Ya'aroch la'Shem Yidmeh la'Shem" (below, 89:7).
Radak: One cannot arrange (list) in front of You all the wonders that You did for us; there are too many. Malbim - this is both for natural acts, and for wonders.
Malbim: This is a Ma'amar Musgar (parenthetical comment). Your natural acts and wonders are nothing for You; they are great only based on our level.
Why did he say "Agidah va'Adaberah"?
Rashi: If I will come to tell, "they are too great to tell."