Sukkos

We end Neilah with the recitation of the posuk "Hashem hu haElokim" seven times. (R' C. Kompel claims that throughout Tanach we find the words "Hashem Hu Elokim" exactly seven times!) The Levush explains that at the end of Yom Kippur we escort Hashem back to his heavenly throne. We recite the verse seven times to escort Hashem through the seven heavens.
When you escort someone you don't just watch him walk off, you walk with him. Yom Kippur ends with us walking Hashem through the heavens to his throne. It is there- at Hashem's side- that we begin the Yom Tov Sukkos. When we sit in the Sukka we are sitting in Hashem's shadow, being embrached by Him- the place where we escorted him on Yom Kippur. My Shvugger Zalmen Leib told me a insight into the Ushpizen that he heard from R' Aron Fogel. What is special about Sukkos that we greet the Ushpizen into our sukka? When we are seated near Hashem in the heavens - which is where our Sukkas are located- who do we expect to meet? - the ones that mingle there all the time, the Ushpizen. They aren't guests at our table, rather we are guests in their world.