The reason behind the term is because jews and christians have exactly the same holy book, they share the same bible, that is the old testament. Also because jews and christians also have the same laws under god, the 10 commandments. The jews and christians are the same people; they split because of the schism over Jesus Christ. Jesus was a jew, a hebrew, and was followed by many other jews. However, not all jews followed him and remained "jewss, but those who followed him broke off from the jews and became christians.