What is the meaning of "[Ein] Tov ba'Adam"?
Rav Sadya Gaon: It is the happiest, best person.
Rashi: This is said in astonishment. Metzudas David - is it not good to eat and drink like he desires, and not skimp in order to leave to his sons after him?
Ibn Ezra: This one who toiled did not find good in all his toil, except for food and drink. A word such as 'Rak' is omitted; it should say Ein Tov ba'Adam Rak she'Yochal v'Yishteh. Similarly, "Ki Einam Yod'im La'asos Ra" (4:17).
Rashbam: Man's only good engagement is to eat and drink, to show good for himself in his toil.
Rid: This is man's only good in this world.
Seforno: The best conduct for man [is to eat what is necessary, and not seek extra].
What is the meaning of "she'Yochal v'Shasah v'Her'ah Es Nafsho Tov"?
Rashi: He should put to his heart to do Mishpat and Tzedakah with food and drink. So Yehoyakim was told "Avicha ha'Lo Achal v'Shasah v'Asah Mishpat u'Tzedakah Az Tov Lo" (Yirmeyah 22:15).
R. Avigdor citing Koheles Rabah: Every eating and drinking in this Sefer refers to Torah and good deeds - "[Le'echol v'Lishtos v'Lismo'ach] v'Hu Yilvenu va'Amalo" (8:15) - do eating and drinking accompany a person to the grave?! Rather, Torah and good deeds accompany him (Avos 6:9).
R. Avigdor: This shows that we make a Seudah when finishing Torah 1 .
Seforno: He should strive with his toil and acquisitions to see good for his Nefesh and eternal happiness. Refer to 2:24:1:6.
Metzudas David: He should do Tzedakah and Chesed with food and drink, to show (bring to) his Nefesh good eternal reward.
Magihah (in Toras Chayim): Koheles Rabah 1:1 learns this from a different source.
Why is "Zo" written with a Hei?
R. Avigdor: This is like it says "ul'Simchah Mah Zo Osah" (2; also there, Zo is written with a Hei). It is Simchah of a Mitzvah. The Hei shows that one who benefits from a Seudah of Simchah of Torah, it is as if he fulfilled the five Semachos in Parashas Re'eh - "v'Achalta Lifnei Hashem Elokecha", "Lifnei Hashem Elokecha Tochalenu", "v'Achalta Sham Lifnei Hashem Elokecha" (Devarim 14:23, 12:18, 14:26), and another two 1 . This explains "Zeh ha'Shulchan Asher Lifnei Hashem" (Yechezkel 41:22).
"Va'Achaltem Sham Lifnei Hashem Elokeichem", "Lifnei Hashem Elokecha Sochalenu" (Devarim 12:7, 15:20).
How is this from Hashem?
Ibn Ezra: The one who gathers money is like a Shomer. He may not touch it until Hashem gives to him permission.
Rashbam: It is from Hashem that man eat and drink; it is not Hevel. However, all the matters that I mentioned above are Hevel.
Ri Kara: If man does good for himself from his toil, this shows that the money came from Hashem to benefit from it; Hashem is pleased with him. He brought to him wealth and property to benefit from it.
Rid: There are people who are stingy even with themselves. Shamayim does not let them rejoice in their toil.
Seforno: This choice (refer to 2:24:2:4), Hashem commanded about it - "u'Le'avdo b'Chol Levavchem uv'Chol Nafshechem; ? v'Achalta v'Savata" (Devarim 11:13, 15). V'Savata (you will be satiated) is what is necessary; it does not say 'you will bequeath to another.'
Metzudas David: Even though it is in man's hand, my intellect saw that it is a gift from Elokim to tilt his heart to this. It seems that most people do not do so.