You are misunderstanding the quote. A man, a Jew, asked Jesus, another Jew, what "command" he should obey, since Jesus was clearly preaching beyond religious obedience and the man was confused. So in reply TO THIS MAN, Jesus said "I give you only one "command", to love God with all your heart, and your brothers as yourself". Hopefully, the man understood.
Jesus only used the term "command" because that's what the man was asking for. Jesus understood that the man couldn't grasp the concept of living by the spirit of love, because he had lived his whole life steeped in religious dogma, laws, and rules. The man couldn't comprehend how to live without the idea of some "divine command". So Jesus responded to the man, kindly, and gave him his "command".
But what Jesus told the man to do; to love, can't really be done as obedience to a command. It has to be done as a voluntary expression of the spirit.
Many here on TOL are like that man. They cannot conceive of a relationship with God that is not based on religion, and on obedience to religious dogmas and rules and laws. Sadly, they can't understand that love is not a form of obedience. And so they go around preaching obedience to their religion, and their religious laws, obsessively, think that this is obedience to and love of God. But are just blend men trying to lead other blind men into the dark. Because Jesus' message was a message of the spirit. Not a message of religious authority, dogmas, or laws.