He was born of a Jewish mother, in Galilee, a Jewish part of the world.
All of his friends, associates, colleagues, disciples, all of them were Jews. He regularly worshipped in Jewish communal worship, what we call synagogues.
He preached from Jewish text, from the Bible. He celebrated the Jewish festivals. He went on pilgrimage to the Jewish Temple in Jerusalem where he was under the authority of priests.... He lived, was born, lived, died, taught as a Jew.
