All those ancient Jews were sent to prepare the coming of one teacher. They are not separate teachers.
That is the best answer that can stop me from wondering how inefficient god was in sending all his messengers to a relatively unpopulated region. If it was only one teacher that God sent 2004 years ago, and all the dudes before and after him are simply not to be considered teachers, then god did not send "ALL" his messengers to one place. He sent only one messenger. The rest are simply philosophers or something?