Of course every Shabbat is a Sabbath of Song, since singing plays such an important part both in the synagogue and at home, on Shabbat and indeed every occasion.
To illustrate the central role of song in Judaism, let me recount the story of a London colleague of mine who spent his career as an educator and writer without holding a synagogal position.
I was told that the reason was that he could not hold a tune and therefore felt at a disadvantage in synagogue life. People wondered why he had this view since he could have chosen to declaim the prayers and scriptural readings rather than chanting them. He might have answered that the music gives a service its rhythm and emotion.
It is not that a minister or rabbi necessarily has to be a cantor, but there are times when there is no option.
However, the original chazan (cantor) was not normally a singer at all. His title is from a Hebrew root that means to see – hence the Book of Isaiah begins Chazon Yeshayahu ben Amotz, which is not the song but the vision of Isaiah the son of Amotz.
True, there is a theory that before printing was invented and manuscript books were rare and expensive, the prayer leader was likely to be the only person who had a siddur, and he became known as “the one who sees”.
An attractive idea, but it is more probable that in the ancient synagogue the chazan was not so much a cantor but an administrator or overseer. The service was conducted by whoever had a pleasant voice, using melodies which developed over the ages but had their beginnings at the time of the Second Temple.
In time the number of experts who could chant the prayers declined and if the overseer had a voice the rest of the congregation knew him well enough to persuade him to conduct the service.