Music and singing were an essential part of the Temple service. According to the Mishnah on today’s daf (=page):
There were never less than twelve Levitesstanding on the platformand their number could be increased into infinity. No minor could enter the Court of the Sanctuary to take part in the service except when the Levites stood up to sing, but they didnot join in the singing with harp and lyre, but with the mouth alone, to add flavor to the music.
In the Gemara, Rav Papa explains that the number of Levites is derived from a passage in I Divrei Ha-Yamim(25:1-9) that mentions nine lyres, two harps and cymbals.
Where did the Levites stand?
As we learned on yesterday’s daf, the dukhan, or platform, was part of the Court of the Sanctuary, in a place that was sanctified for use during the sacrificial service. According to the Mishnah in Masechet Middot (2:6) the dukhan was a platform that extended the entire width of the court at the beginning of the area of the Priestly compound (ezrat kohanim). It was from here that the priests would bless the people. There is an alternative explanation that suggests that the Levites would sing from the 15 steps that led from the ezrat nashim to the ezrat yisra’el, which was also called the dukhan.
According to Rashi, the reference to the Levites is to their a cappella singing without instruments, but Tosafot argue that this is teaching about the Levites who are playing their musical instruments, as, indeed, is the implication of the Gemara.
As the Mishnah indicates, minors were not permitted to perform the ordinary functions of the Levites – serving as doorkeepers or cleaning the sanctuary – they could only join their elders since their voices added to the beauty of the music.