What are the many interpretations of the Four Species waved during Sukkot services? This source sheet, based heavily on one by Sarah Jaffe Kasdan, lays out several classic Rabbinic interpretations and two moderns ones. I have added the question of "What does it mean to hold these in our hands, metaphorically?"
The Netivot Shalom's essay on Sukkot as a Day of Bliss, addressing the question: Why is Sukkot called The Season of our Joy. This is my translation with the sources referenced included from Safaria.