Charles Ellicott Commentary Leviticus 23:35

"On the first day shall be a holy convocation: ye shall do no servile work." — Leviticus 23:35 (ASV)

on the first day shall be an holy convocation. — At daybreak on this day, one of the priests, accompanied by a jubilant procession and a band of music, went with a golden pitcher to the pool of Siloam. After filling it with water, he returned with it to the Temple in time to join his fellow priests in the morning sacrifices. He entered from the south through the water-gate and was welcomed by three blasts of the trumpets. He then ascended the steps of the altar with another priest, who carried a pitcher of wine for the drink offering.

The two priests turned to the left of the altar, where two silver basins were fixed with holes at the bottom, and simultaneously poured the water and the wine into their respective basins in such a way that both were emptied at the same time onto the base of the altar. This ceremony of drawing the water was repeated every morning during the seven days of the festival. Another jubilant multitude, which had gone outside Jerusalem at the same time to gather willows, then returned. With great rejoicings and amid blasts of trumpets, they carried the willows into the Temple and placed them at the altar in such a way that their tops overhung and formed a kind of canopy.

Ye shall do no servile work therein. — For the difference between servile and necessary work see Leviticus 23:7.