What is the structure of this Mizmor?
Rashi (26): It has 26 verses, corresponding to the 26 generations from creation until Matan Torah. Each verse ends "Ki l'Olam Chasdo." Hashem sustained [those generations] in His Chesed. Radak #1 - there was no Torah to be fed due to it 1 . Even though only Yisrael accepted the Torah, the entire world stands in Yisrael's merit.
Radak #2: There are 26 verses, for the Mizmor discusses 26 matters.
They were commanded the seven Mitzvos of Bnei Noach! And also the rest of the Torah, even before they were commanded, Hashem rewarded for guarding "Mishmarti Mitzvosai v'Sorosai" (Bereishis 26:5)! Perhaps since only a few individuals knew Torah, it was not enough to sustain the generation. (PF)
Who should thank Hashem?
Radak: The entire world. Malbim - after commanding to praise and bless Hashem (in the previous Mizmor), he commands to thank Him for the goods that they received from Him, due to His good and His Chesed.
What is the meaning of "Ki l'Olam Chasdo"?
Radak: He is good, and His Chesed does not cease; it is forever. This is repeated in every verse, to increase the praise.
Malbim: His Chasadim are both when He conducts the world based on nature, and when based on miraculous conduct - "Hashem Shimcha l'Olam Zichrecha l'Dor va'Dor" (135:13) refers to these two ways.
