What is "Yisron"?
Rashi: It is reward and benefit. Ibn Ezra - its grammatical form is like "Zichron" (11). It is a noun. The first letter of the root (Yud) is sometimes omitted, like we find in Pi'el conjugation 1 .
Rashbam: All this applies to below "Ein Tov ba'Adam she'Yochal v'Shasah" (2:24). All man's actions are Hevel. There is no good act for man to enjoy, only to drink and rejoice in his portion.
Magihah (in Toras Chayim): E.g. there is a Vov in place of the Yud - Hosarti, Osir
What do we learn from "b'Chol Amalo"?
Koheles Rabah (1:3, partially cited in R. Avigdor): Chachamim wanted to bury Sefer Koheles, for it has matters leaning to heresy 1 ! Is there no gain for man even in his toil in Torah?! They retracted - it does not say b'Chol Amal, rather, b'Chol Amalo, to exclude toil in Torah.
Why is there no gain for man under the sun?
Rashbam: In the end, man passes from the world.
Why does it say "Tachas ha'Shamesh"?
Shabbos 30b: There is gain from toil in what preceded the sun, i.e. Torah.
Rashi: In place of Torah, which is called light - "v'Sorah Or" (Mishlei 6:23). Any toil that one does in place of engaging in Torah, what reward is in it?!
Ibn Ezra: This is time, which passes. It depends on the sun. Daytime is from sunrise to sunset, and night is from sunset to sunrise, whether or not the moon and stars are seen. Also "Zera v'Katzir v'Kor v'Chom v'Kayitz va'Choref" (the seasons) (Bereishis 8:22) depend on the sun leaning to the north or south (it rises and sets to the north [of east and west, responsibility] in summer, and to the south in winter). Even though the moon affects rivers and moist vegetation, its effect is tiny compared to the sun's. There is Yisron in seeking Chachmah to be clarified to the Ru'ach, for it is not Tachas ha'Shamesh (bounded in time).
Rashbam: This is based on "Ein Nistar me'Chamaso" (Tehilim 19:7). It is as if it says Tachas ha'Shamayim.
Seforno: This refers to matters that do not endure. Why should Tzelem Elokim toil so much for such things?!
Metzudas David #1: This is toil to gather acquisitions under the Ma'arachah of Shamayim. It mentions the sun, for it has the greatest effect on lower beings, and it is the greatest [matter in the Ma'arachah. The Ma'arachah] is called Meleches ha'Shamayim ("Lekater li'Mleches ha'Shamayim" - Yirmeyah 44:17), an expression of Meluchah (kingdom). Why should one toil for them? Tomorrow, the one who gathered them will die, and not take anything with him!
Metzudas David #2: In this world, where the sun rises, what benefit is there in gathering acquisitions?
