Who is Mr. Goldstein from The History of Love and what is their importance?

Mr. Goldstein is the janitor at Bird's school. Bird befriends the man and talks to him at length about the Jewish faith. It is Mr. Goldstein that tells Bird about the lamed vovniks, the 36 holy people that are responsible for the world's existence. When he takes ill suddenly, Bird feels that he has disappointed Goldstein so greatly that it has made him sick, and Bird decides that he will go about making his friend proud.