The Haftarah for the first day of Sukkot is the prophecy of Zecharya concerning the war of Gog and Magog, which will climax with the final redemption and acknowledgment by the nations that Hashem alone is the King, and that Israel is His people. This realization will be celebrated on Sukkot, for, according to the prophecy, the surviving nations will join the Jewish people every year in celebrating the Sukkot festival.
Zecharya’s reference to the sukkah is an allegory. He does not mean that in Messianic times the Noahides will be obligated to eat in the sukkah together with the Jew, and be punished if he does not fulfill the mitzvah. He means that the Noahides will be expected to practice the lesson conveyed by the mitzvot of the festival of Sukkot. They must forsake their striving for selfish gain and replace it with a sense of responsibility and sharing of privileges with all of humanity. Hence, Zecharya’s words, “Lo ya’alu lachog et chag haSukkot” — “They have refused to go up to celebrate the festival of Sukkot” — can be explained to mean that they have refused to elevate themselves spiritually and realize the message that Sukkot teaches humanity.