Why is the mitzvah of the four species especially appropriate for the holiday of Succot?

Question

What connection is there between the mitzvah of the four species and the theme of Succot? Why is this mitzvah especially appropriate for this holiday specifically?

I am aware that there are different opinions regarding what idea the Succah represents; a connection to any one of them is fine.

Answer 1

Here's one possibility: The Rosh (Succah chapter 3:26) quotes a Midrash that the taking of the four species is a symbol of our joy at being judged favorably and exonerated on Rosh Hashanah [and Yom Kippur] (see also the Yerushalmi brought there).

The Gr"a (Shir Hashirim 1:4) gives a reason why Succot is celebrated specifically on the 15th of Tishrei: That is the day the Clouds of Glory returned after the sin of the golden calf, signifying God's forgiveness.

So both the Succah (representing the Clouds of Glory) and the four species share a common theme of being forgiven for our sins and judged favorably by God during the preceding days of judgement (Rosh Hashanah and Yom Kippur).

Answer 2

The Mishnah in Rosh Hashanah says that on Sukkos is the judgement for water.

On four points the word is judged...and on Chag (Sukkos) we are judged on water.

The Talmud there explains that the special water libation that was brought on Sukkos was brought so that we would be blessed with rain in the coming rainy season (which occurs after Sukkos).

Rabi Yehudah said in the name of Rabi Akiva "...and why did the Torah say to pour the water on Chag (Sukkos), the Honly One blessed be He said, 'pour before Me water on Chag so that you the rain of the year is blessed for you.'

This relates to the reason we bring the four species as is explained in the Talmud in Taanis:

Rabi Eliezer said, 'Since the four species are only to appease on the water. Just like these four species can't be had without water, so to the world can't exist without water.'

As we can see, one of the major themes of Sukkos brought in the Talmud, is rain. Sukkos comes right before the rainy season. On Shemini Atzeres as well, we start mentioning rain in the second blessing of the Shemoneh Esreh (according to another Talmudic opinion, we should be starting on Sukkos). We have the special water libation as well. So taking the four species is very appropriate for the time.