leviticus 23:34 Speak unto the children of Israel, saying, The fifteenth day of this seventh month shall be the feast of tabernacles for seven days unto the LORD. - Free Bible Online

      34-44. the feast of tabernacles, for seven days unto the Lord--This festival, which was instituted in grateful commemoration of the Israelites having securely dwelt in booths or tabernacles in the wilderness, was the third of the three great annual festivals, and, like the other two, it lasted a week. It began on the fifteenth day of the month, corresponding to the end of our September and beginning of October, which was observed as a Sabbath; and it could be celebrated only at the place of the sanctuary, offerings being made on the altar every day of its continuance. The Jews were commanded during the whole period of the festival to dwell in booths, which were erected on the flat roofs of houses, in the streets or fields; and the trees made use of are by some stated to be the citron, the palm, the myrtle, and the willow, while others maintain the people were allowed to take any trees they could obtain that were distinguished for verdure and fragrance. While the solid branches were reserved for the construction of the booths, the lighter branches were carried by men, who marched in triumphal procession, singing psalms and crying "Hosanna!" which signifies, "Save, we beseech thee!" (Ps 118:15, 25, 26). It was a season of great rejoicing. But the ceremony of drawing water from the pool, which was done on the last day, seems to have been the introduction of a later period (Joh 7:37). That last day was the eighth, and, on account of the scene at Siloam, was called "the great day of the feast." The feast of ingathering, when the vintage was over, was celebrated also on that day [Ex 23:16; 34:22], and, as the conclusion of one of the great festivals, it was kept as a sabbath.

JFB.