This is a quote from the Letter from Birmingham Jail, by MLK Jr, quoted in John Piper’s weekly email, Fresh Words. You can read it all at desiringgod.org.
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 ideas and principles of popular opinion; it was a thermostat that transformed the mores of society. . . . But the judgment of God is upon the church [today] as never before. If today’s church does not recapture the sacrificial spirit of the early church, it will lose its authenticity, forfeit the loyalty of millions, and be dismissed as an irrelevant social club with no meaning for the 20th century. (Letter, p. 17)