Charles Ellicott Commentary Leviticus 23:34

"Speak unto the children of Israel, saying, On the fifteenth day of this seventh month is the feast of tabernacles for seven days unto Jehovah." — Leviticus 23:34 (ASV)

The fifteenth day of this seventh month. —This refers to the month Tishri, which corresponds to the end of September and the beginning of October, and is only four days after the Day of Atonement.

Shall be the feast of tabernacles. —The law here gives no directions on how or where these tabernacles are to be erected. The details, as in many other enactments, are left to the administrators of the Law. From the account of the first celebration of this festival after the return from Babylon, the Jews, following the command of Ezra, made themselves booths on the roofs of houses, in the courts of their dwellings and of their sanctuary, and in the streets of the Water Gate and the Gate of Ephraim.

They made these tabernacles from olive branches, pine branches, myrtle branches, palm branches, and branches of thick trees (Nehemiah 8:15–18).

The construction of these temporary dwellings, however, was more minutely defined by Ezra’s successors. During the Second Temple period, it was ordained that the interior of each tabernacle must not be higher than twenty cubits and not lower than ten palms. It must also have at least three walls, with a thatched roof partially open to allow a view of the sky and the stars.

It must not be under a tree, nor covered with a cloth or any material that can become defiled. Only branches or shrubs that grow out of the ground are to be used for the covering.

The Israelites began to erect these booths on the day after the Day of Atonement. On the fourteenth, which was the day of preparation, the pilgrims came up to Jerusalem. On the eve of the festival (the fifteenth), the priests proclaimed the approach of the holy convocation with blasts of trumpets.

As on the feasts of Passover and Pentecost, the altar of burnt offering was cleansed in the first night watch. The gates of the Temple, as well as those of the inner court, were opened immediately after midnight. This was for the convenience of the priests who resided in the city and for the people, who filled the court before the rooster crowed to have their sacrifices duly examined by the priests.