He was born into a Jewish family and community and was raised as a jew and almost certainly lived as a jew until he began his ministry. However once he began his ministry he often spoke out AGAINST many jewish practices and beliefs and was rejected and prosecuted by the Jewish leadership. The second definition of 'rabbi': is a Jewish scholar, a scholar qualified to teach or interpret Jewish law. In this sense he was a rabbi. We see him teaching other rabbis already at age twelve and this almost certainly continued through his adulthood - until he began his broader ministry.