הבלים אמר קהלת הבל הבלים הכל הבל – In the six days of the creation of the world, the Shem Hashem, "אלקים" is mentioned 32 times K'neged the 32 levels of wisdom with which the world was created. (Perhaps these 32 times represent the "לב", the heart. The purpose of creation is to serve Hashem with our heart.) On the seventh day of creation it says "אלקים" three times K'neged the 3 Shabbos Seudos one should have. Shlomo Hamelech mentions "אלקים" 40 times K'neged the 40 days it takes for the formation of a fetus to teach us that the main purpose of the creation of the world was for man.
Now we can understand the reason for the double L'shonos of "הבל", and why we Lain Koheles on Sukkos. Rosh Hashana and Yom Kippur are a time to serve Hakodosh Boruch Hu through Yirah, fear. After we have attained Yiras Shomayim, we then must work on our Ahavas Hashem. On Sukkos, we go outside of our permanent dwellings and live in a temporary one. We demonstrate that this world really is Hevel Havalim. This world is not the true world; it is a way to get to the next world, the true world. The Ribbono Shel Olam, in His infinite mercy and love for Klal Yisroel, gives us Mechila and Kapparah during the Yomim Nora'im. We must return that love to Hakodosh Boruch Hu. The Posuk repeats the word "הבל" stressing that we must not only serve the Ribbono Shel Olam with our bodies, but we must also serve him with "הלב" – our hearts. May we be Zoche to Madreiga Ahavas Hashem.