The chazan leads the prayer service. Sometimes, the whole congregation says the prayers together with him while he sets the pace; other times, he recites the prayers and the congregation responds Amen, such as in Chazarat HaShatz (repetition of the Amidah) and the recital of the Kaddish prayers. Hence, the chazan must be an upright, highly regarded, humble, amiable person, who has a pleasant voice and is accustomed to reading the Torah, Nevi’im (Prophets) and Ketuvim (Sacred Writings) (Ta’anit 16a; Shulchan Aruch 53:4).
We must be especially meticulous about this on the High Holy Days, and on fast days, when we pray to Hashem and beg Him to forgive us for our sins, save us from our troubles, and bring our redemption closer. For if there is fault in the chazan, the congregation’s prayer will not ascend properly (Rama 581:1).
During Chazal’s time, it was forbidden to write siddurim because only the written Torah (Torah Shebichtav) was permitted to be written down. Anything that was transmitted by word of mouth, including the prayers and blessings instituted by the Chachamim, was forbidden to be put into writing (Temurah 14b). At that time the chazan’s task was very important because all the prayers had to be recited aloud in order to fulfill the obligations of the congregation. Therefore, the congregation designated one chazan for this honorable task, and all the laws that apply to appointing the chazan on fast days also pertained to the regular chazan. L’chatchilah, each and every person in the congregation would have to agree to the chazan‘s appointment, since he fulfilled everyone’s obligation. However, today, when everyone has a siddur, the chazan‘s job is less important and selecting a permanent chazan for the whole year is no longer customary. Instead, every day a different person can lead the prayer service; therefore we are less meticulous in choosing a chazan (Shulchan Aruch 53:19; Mishnah Berurah 53:53).
Even so, when appointing chazanim, the gabba’im (synagogue coordinators) must try to choose decent people who abide by the Torah and observe the mitzvot. They should be people whom the congregation agrees to have as its prayer leaders, for the chazanim are the ones who repeat the Amidah and recite the Kaddish prayers on its behalf (see Kaf HaChaim 53:86). Additionally, on Shabbat and festivals, when it is customary that the chazanim sing and chant part of the prayer service, the chazanim should be musically gifted with pleasant voices.