3,911. Five Years of Study

Hilchos Klei HaMikdash 3:6

Twelve times a year the flute was played before the altar: when slaughtering the Pesach offering, when slaughtering the “second Passover” offering, on the first day of Pesach, on the first day of Shavuos, and on all eight days of Succos. Playing the flute on these days overrides normal Shabbos restrictions. This is because it’s done with an offering. This makes it part of the Temple service, which overrides normal Shabbos restrictions.

Hilchos Klei HaMikdash 3:7

A Levi may not enter the courtyard to serve until he has studied for five years. This is learned from Numbers 8:24: “This shall be for the Leviim from the age of 25,” while Numbers 4:30 says, “From the age of 30....” We infer that they study for five years and don’t actually serve until they are fully grown as per Numbers 4:19: “Each man to his service.”