Martin Luther King Jr.

Not just a great civil rights leader, but a man of faith in the indiscriminant love of Jesus Christ. He believed in the power of the church to bring about societal change. In his 1963 letter from jail in Birmingham, he challenged local clergy -

“There was a time when the church was very powerful. It was during that period when the early Christians rejoiced when they were 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."

That challenge still echos to us today. We can't just stand around and tell the world that it's messed up. We must do something to bring people to the Healer.
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Here's an interesting article from Relevant's website.
More MLK links:
Audio & text of "I Have a Dream" (with some video excerpts)
Text only of "I Have a Dream"