Positive commandment · Mitzvat Aseh #16 of 613
To gather all of Israel on the festival of Sukkot
לְהַקְהִיל אֶת הָעָם לִשְׁמֹעַ תּוֹרָה בְּמוֹצָאֵי שְׁבִיעִית
The verse · Devarim 31:12
הַקְהֵל אֶת־הָעָם הָאֲנָשִׁים וְהַנָּשִׁים וְהַטַּף וְגֵרְךָ אֲשֶׁר בִּשְׁעָרֶיךָ לְמַעַן יִשְׁמְעוּ וּלְמַעַן יִלְמְדוּ וְיָרְאוּ אֶת־ה׳ אֱלֹהֵיכֶם וְשָׁמְרוּ לַעֲשׂוֹת אֶת־כׇּל־דִּבְרֵי הַתּוֹרָה הַזֹּאת
“Gather the people together, men, and women, and children, and thy stranger that is within thy gates, that they may hear, and that they may learn, and fear the Lord your God, and observe to do all the words of this Tora:”
The Rambam’s words
To collect the people to hear the Torah [being read] in the year following the shemitah year, as [Deuteronomy 31:12] states: "Gather together the people."
לְהַקְהִיל אֶת הָעָם לִשְׁמֹעַ תּוֹרָה בְּמוֹצָאֵי שְׁבִיעִית, שֶׁנֶּאֱמָר: "הַקְהֵל אֶת הָעָם..." (דברים לא, יב).
Why · Sefer HaChinuch #612
To gather all of Israel on the festival of Sukkot
“It is from the roots of the commandment [that it is] because the entire essence of the people of Israel is the Torah; and through it are they separated from every nation and language, to be meritorious for life of the forever — eternal pleasure that is not surpassed by anything among the creatures.”
Who & when
“This commandment is practiced at the time when Israel is on their Land.”
Where in the Mishneh Torah
Hilchot Festival Offering הלכות חגיגה