Leviticus 23:35

On the first day [shall be] an holy convocation
When they should be called together to holy exercises, to prayer, praising, and reading the law; and at this present time they observe this day, by rising early in the morning and going to the synagogue, where they sing and pray much; and everyone takes a bundle of branches of palm tree, olive in the right hand, and a pome citron in the left, and says, blessed be thou, O Lord our God, the Lord of the world, who has sanctified us by thy precepts, and hath commanded us to carry the palm tree bundle; then they shake it, and give a great shout, according to ( Psalms 96:12 ) ; all which they frequently repeat on this day, as well as bring out the book of the law, attended with various ceremonies, and read some passages in it ^F20:

ye shall do no servile work [therein];
as on the first and seventh days of unleavened bread, the day of Pentecost, and of the blowing of trumpets; but what was necessary for preparing and dressing food might be done.