Halakhah su Geremia 12:78

The chazzan must be a worthy person for it is said: [God says of His nation]: "She raises her voice at Me, I therefore, have contempt for her,"²⁸Jeremiah 12:8. and our Rabbis of blessed memory, said, that this refers to an unworthy chazzan who, [nevertheless,] goes down to the Amud.²⁹The Amud is the Reader’s Desk in the synagogue. Who is considered worthy? One who is free of sin and who is respectful, that is, his reputation is untarnished, and was unblemished even during his youth; and one who is humble and acceptable to the congregation so that they agree that he lead the prayers. He should have a pleasant and a sweet voice, which draws [appeals to] the heart, and he should be one who regularly reads the Scriptures, so that the verses in prayer are fluent in his mouth. If a person cannot be found with all these attributes, [then] they (the congregation) should choose one among them who excels in wisdom and good deeds.

Ḥazanim must have kavana that their singing is the sake of heaven. If they prolong their ḥazanut (cantorial virtuosity) with the sole purpose of showing off their beautiful voices, the Torah states about them, “They have raised their voice against Me, so I hated them” (Yirmiyahu 12:8). They are using the holy prayer service to self-aggrandize. Even one whose sole intent is for the sake of heaven should not prolong his singing, so as not to burden the congregation (Rashba; SA 53:11).

“Thou art near in their mouth and far from their reins” (Jer. 12:2). These are the people who deliberately attribute sin, obscenity and evil things to their friends and then say, “May the Lord forgive us.” These people are not in the class of the God-fearing, for they do not fear sin. Nor is the rod of God and His awe upon them so that they might be able to restrain themselves and not utter evil. While it appears in their eyes that He pardons them when they say, “May the Lord forgive us,” God will not want to forgive them for they know Him (what He expects of them) and (nevertheless) they intend to rebel.¹Shabbath 116a.