John 7:15

‘The Judaisers therefore marvelled saying, “How does this man know letters, having never learned?” '

As they listened to Him even His enemies were impressed. They were amazed. They could not understand how He had such wide knowledge and understanding of the Scriptures when He had never been through the Rabbinical schools. His wide knowledge of the Scriptures and of current ideas about them impressed them and for a while held them back from acting against Him. Jesus thus taught many things of which we may well know nothing.

‘Know letters' - to have the ability and training to be a teacher. ‘Never learned' - had not been through the Rabbinical schools.