The teacher of Israel (ο διδασκαλος του Ισραηλ). The well-known or the authorized (the accepted) teacher of the Israel of God. Note both articles.

And understandest not these things? (κα ταυτα ου γινωσκεισ;). After being told by Jesus and after so propitious a start. His Pharisaic theology had made him almost proof against spiritual apprehension. It was outside of his groove (rote, rut, rot, the three terrible r's of mere traditionalism).