In his defense Jesus said to them, “My Father is always at his work to this very day, and I too am working.” For this reason they tried all the more to kill him; not only was he breaking the Sabbath, but he was even calling God his own Father, making himself equal with God.
It was a matter of dispute among the Rabbis as to whether God continued to rest on the seventh day. Eventually, by the end of the first century the majority accepted Jesus' point that God does not stop working. However, here as elsewhere in this gospel Jesus makes himself 'equal with God and this is blasphemy to them.
Jews, Muslims, JWs and Mormons are all caught in the same blasphemous trap; the failure to recognize Jesus as God. Are you?