Jesus answered: "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 first commandment. And a second is like it: You shall love your neighbor as yourself."
The corporate church world has generally made this a foundation for the Christian life. But the key words in the question that Jesus answered was "in the law" ... referring to the law of Moses which was still in effect at that time for Israel. But it is a law Gentiles were never under and was made obsolete for Israelites after the cross and resurrection. It is a commandment no one had ever kept nor has anyone successfully fulfilled it since. The "great commandment" is not the message of the gospel as suggested by those who blend the Bible into one book as if two very different and incompatible covenants were meant to be mixed together. Love is still the answer—but in a very different context.