And then he summarized this by saying "On these two commandments hang all the law and the prophets," which means the entirety of religious practice is either fulfilled, or failed on those two injunctions. Why? Because love works no ill. If one first loves God and is filled with God, then will naturally do no harm to another. They will not bicker who has the right beliefs, because Love is the fulfillment of the nature of God in the world.
Seemingly little except for the core of his teachings?
Indeed. :yes: As I repeatedly say, people (including Christians) cherry-pick what they want from his teachings to "prove" their point without knowing what the teachings really are and their purpose. That's why I said 'seemingly'... it's a surface view. His teachings cannot be taken at face value, and out of context.