Why is The Last Supper By Leonardo da Vinci significant?

Actually, the Last Supper was a common theme at the time.

[It portrays the famous speech made by Jesus Christ when he told his prediction that one of his closest men (Judas) would betray him.]

The reason Leonardo's painting really became famous is that it was painted on a wall in what was then the dining hall of a monastery and Leonardo showed Jesus and the disciples sitting among the other diners, sort of like the head table. He showed the actual everyday plates, cups, and linens that the monks were using then, putting Jesus in the same place-- doing the same things-- as the monks, which was unique. Elsewhere, Jesus was shown as separate or living in a distant land, elevated from the common people.