The very command to love him that you quote is the call of God, a revelation of his desire to have a personal relationship with us. But he calls for the love above all other loves because God alone is God, and only God has the right to it. Christians believe that God’s highest revelation of himself and his love came to earth in the person of Jesus Christ. “For God so loved the world that he sent his only Son into the world, that whoever would believe in him should not perish, but have eternal life.” (John 3:16)
Love then is a drive inside us that wants to give (rather than get) which causes the lover to humble himself and submit himself to his beloved in order to serve his beloved. You can serve someone without loving that person—for pay, out of fear, for fun—but you cannot love without serving. Ultimately to love God is not about how it feels, it’s about what you do, whether you will lay down your life in loving service to God through doing loving service toward others (You shall love your neighbor as yourself). Jesus said that all the law and the prophets hang on these two commands.
I hope that helps.