Would you please elaborate on the mitzva of rejoicing on Succot?
When the Temple stood, there was a special ceremony of rejoicing called “simchat beit hashoeva” which was associated with the drawing of water for the purpose of the special Succot water-libation and involved dancing by firelight throughout the night. All of Israel rejoiced to a point where Divine inspiration flowed down upon the participants celebrating in the Temple courtyard and many experienced prophecy.
Now that the Temple is in ruins as a result of our sins, we have neither the altar, nor sacrifices, nor libations. Nevertheless we are commanded to rejoice in the festival of Succot as in the verse, “And you shall rejoice in your Festival” (Deut. 16:14). Therefore it is customary in many Jewish communities to gather during the nights of Succot in the synagogues to sing and dance together in memory of simchat beit hashoeva. This is usually accompanied by live music, attended by men, women and children, and continues into the wee hours of the morning. Customarily, the festivities are preceded with a recital of the fifteen “Songs of Ascent” composed by David in Psalms 120-134. These correspond to the fifteen steps in the Sanctuary upon which the Levites stood as they played music and sang during the simchat beit hashoeva of Temple times.
Another form of rejoicing on the holiday is through festive meals. However, when one eats and drinks, one is obligated to simultaneously provide for the needs of the stranger, the orphan, the widow and the poor (ibid). One who indulges in food and drink with his family but does not invite the lonely and the needy to join in the festivities is considered to be not rejoicing in the holiday but rather rejoicing in his belly. In addition, while making festive meals in the name of rejoicing in the holiday, he must not be drawn through food and drink to frivolity and levity. Indulgence and intoxication brings foolishness and is not the type of pure joy appropriate for the holiness of the festival. Rather one must direct the pleasure of the meals to delighting in G‑d and the mitzvot by sharing words of Torah at the table, singing songs of praise to G‑d and acting in a way becoming of the holy succah.