Although Jesus is identified as being from Nazareth, he begins his public ministry in Capernaum, which is thought to be the hometown of his first four "fish" disciples: Peter, Andrew, John, and James. As Mark notes at the outset of today's gospel text, they i.e. Jesus and his four new disciples journey to Capernaum to observe the Sabbath (verse 21). Although the NRSV translation doesn't highlight it, the force of the Greek is to suggest that there's a repetitive pattern to Jesus' behavior: that going to the synagogue and teaching there was in fact Jesus' customary practice.
The first century synagogue, as opposed to the temple, was a place to study Torah. It was in the synagogue that scholars (scribes and rabbis) offered instruction and interpretation of the Hebrew Scriptures. But when Je…