What is "Havel Havalim"?
Refer to 1:2:1:1-5.
Why does it say "Amar Koheles" in the middle?
Refer to 1:2:2:1-3 and the note there.
What do we learn from "ha'Kol Hevel"?
Refer to 1:2:4:1-3.
What is the significance of the different vowels in the first and last Hevel in our verse?
Ibn Ezra #1: The first is [a noun] with the same grammatical form as "Zahav"; the second is like Eretz. The latter vowel in the first changes to a Tzeirei because it is Samuch, like "Chalev Izim" (Mishlei 27:27).
Ibn Ezra #2: The first is a command, like Azov (abandon; consider it worthless).
The second verse of the Sefer said similarly. Why is it repeated here?
Ibn Ezra: After mentioning man's death, what I said at the beginning "Havel Havalim" is clarified to you.
Rashbam: Now the Sefer is completed. Those who arranged it 1 wrote from here until the end.
Seforno: From all this is clarified the tiny importance of things that perish. Their purpose is not important, and it is not the ultimate purpose [of man].
Metzudas David: The one who arranged the Sefer, he says that Melech Shlomo, who gathered the opposing opinions, properly warned Lehahvil (consider worthless) the Havalim that are totally Hevel, without a proper purpose (but not those that have a proper purpose). Since man's end [is to die], this shows that all is Havel Havalim.
Bava Basra 15a: Chizkiyah and his entourage arranged Koheles.
Above (1:2) it says "Koheles". Why does it say here "ha'Koheles"?
Ibn Ezra: Here, Koheles is an adjective (one who gathers); Hei ha'Yedi'ah (to identify) is not prefixed to a name.
Rashbam: Ha'Koheles is the Chacham.
Rid: The Hei is extra.