Jesus’ enemies would no doubt have liked him to identify as the “greatest commandment” something that would allow them to show that he was mistaken, and that people needed to look to them as the authority on Scripture rather than Jesus. But his answer, summing up all the law in love for God and for neighbor, so clearly demonstrated his spiritual wisdom that they had nothing more to say.
Love for God may sometimes be difficult to delineate. Is it religious devotion? Faithfulness to a creed and set of religious practices? We may often judge ourselves, or others, too harshly or too lightly in this regard. But loving our neighbors as ourselves is a different kind of challenge – we know what to do but so often fall short in doing it.