The Scribes had determined that the Jews should obey 613 precepts. Most of them were man-made laws – 365 negative and 248 positive. They loved discussing which was the greatest. Trying to trip Him, they asked Jesus, and His answer came quickly.
 
Mark 12:30-31 And thou shalt love the Lord thy God with all thy heart and with all thy soul, and with all thy mind, and with all thy strength: this is the first commandment. And the second is like, namely this, Thou shalt love thy neighbor as thyself. There is none other commandment greater than these.
 
Jesus said love, because love is the fulfilling of the law (Romans 13:8). We don’t live by rules but by relationships, a loving relationship to God that enables us to have a loving relationship with others. God is love.