3,932. When a Kohein First Serves

Hilchos Klei HaMikdash 5:15

As soon as a kohein reaches the age of majority, he is able to serve in the Temple, but the other kohanim wouldn’t let him do so until the age of 20. He should only enter the courtyard to serve for the first time when the Leviim are singing.

Hilchos Klei HaMikdash 5:16

A kohein doesn’t serve in the Temple until he has brought a flour offering of one-tenth of an ephah* of his own property, which he offers himself. The same is true for serving as the Kohein Gadol. This is as per Leviticus 6:13: “This is the sacrifice of Aaron and his descendants that they shall offer to Hashem on the day they are anointed.” If a kohein serves before bringing this offering, or if a Kohein Gadol serves as a Kohein Gadol before bringing this offering, the service is nevertheless valid.

*An ephah is a little more than seven gallons.