Who is Rabbi Asher ha-Gassi from The Source; a Novel and what is their importance?

Asher is a rabbi in Makor in 330 C.E. and is a descendant of the Family of Ur. He is unpaid and supports his family by working in the groats mills. He has the stone cutter finishing the interior of the synagogue. He travels to Tverya to work on the formulation of the Laws which will govern how the Jewish people live and work no matter where they are.