Jesus gave it as law...
Matthew 22:36-39 (NASB) "Teacher, which is the great commandment in the Law?" And He said to him, " 'YOU SHALL LOVE THE LORD YOUR GOD WITH ALL YOUR HEART, AND WITH ALL YOUR SOUL, AND WITH ALL YOUR MIND.' "This is the great and foremost commandment. "The second is like it, 'YOU SHALL LOVE YOUR NEIGHBOR AS YOURSELF.'
A law only He kept sufficiently, that He may be gracious to us.