Chazan—the emissary of the congregation חזן ושליח ציבור
He does not perform; he represents: he prays aloud for those who cannot do it themselves. The Talmud lists whom to send before the ark, and a voice is not first on the list.
"The emissary of the congregation discharges the many of their obligation," says the Mishnah. That is the whole point of the office: where a man cannot do it himself, the one sent speaks for him, and the words count for those who sent him. Hence the strictness about whom to send.
Whom to send. The Talmud in Taanit lists, for a public fast: a man used to prayer, whose house is empty and whose hearth is cold, so that he knows want from within; who has children and nothing to feed them; whose youth is clean, who is humble, acceptable to people and able to chant. The voice is named last—after a life one need not be ashamed of.
How it changed. While everyone knew the prayers by heart, the chazan was needed for the unlettered; when communities grew rich, a salaried office appeared, and with it what the rabbis lamented: a chazan who draws out a tune for its beauty while the congregation waits. Between "praying for them" and "singing before them" runs the whole history of this office, and the argument about it is not over.
On the timeline
Related
Sources
Chazal: Mishnah, Talmud, midrash, Zohar
- Mishnah Rosh Hashanah 4:9 — the emissary of the congregation discharges the many
- Taanit 16a–b — whom they set before the ark on a public fast, and why
Basis: Talmud and midrash.