He was teaching and healing. Luke 13:10

“Our Lord Jesus spent his Sabbaths in the synagogues, v.10. We should make conscience of doing so, as we have opportunity, and not think we can spend the sabbath as well at home reading a good book; for religious assemblies are a divine institution, which we must bear our testimony to, though but of two or three. And, when he was in the synagogues on the sabbath day, he was teaching there—en didaskon. It denotes a continued act; he still taught the people knowledge. He was in his element when he was teaching.