God made a covenant with His people, and He meant it as a blessing to all peoples on the face of the earth. The Jews were given the Law to carry a message for the whole world through their inability to be worthy of being the Chosen people.
Jesus came out of those people and was an extension of the providence of that people and God's plan. Jesus didn't give a law, but the standard resides in and comes from Him. People had to learn to think universally, and this was the seedbed on which Christianity grew.
(Hillsdale College - Ancient Christianity)