What does Dr. King mean when he says “In those days the church was not merely a thermometer that recorded the idea and principles of popular opinion; it was a thermostat that transformed the mores of society.” The full context is “There was a time when the church was very powerful—in the time when the early Christians rejoiced at being deemed worthy to suffer for what they believed. In those days the church was not merely a thermometer that recorded the idea and principles of popular opinion; it was a thermostat that transformed the mores of society.”