Best known as a key witness in the famous Mississippi Burning trial that followed the high-profile deaths of three activists during the summer of 1964, Rev. Charles Johnson is one of the South's last remaining Civil Rights leaders and activists.

A native Floridian, Johnson was called "into the turmoil going on in the state of Mississippi as a minister fresh out of college," he says. Now 74, he has been a pastor at Fitkin's Memorial Church of the Nazarene in Meridian, Miss., since 1961, and his decades of activism in the state are documented in Called to the Fire: A Witness for God in Mississippi; The Story of Dr. Charles Johnson (Abingdon Press, Jan.) by his friend and fellow Nazarene pastor Chet Bush.

"When I went to Mississippi, I thought I would see black people hanging from street lamps," Bush quotes Johnson saying about his arrival there. Johnson's fear of moving to the Jim Crow South underscored that "he had to really surrender himself to the call of God in his life in order to be willing to go there," Bush said in an interview with The Tennessean.

The young minister's arrival coincided with the Freedom Rides and the dawn of Civil Rights activism in the state. Michael Schwerner, James Chaney, and Andrew Goodman began to organize and register black voters through collaborations with local pastors. Schwerner and Johnson worked closely together for a few months, boycotting a store and picketing against police brutality at City Hall. In response to such activism, the Ku Klux Klan started firebombing churches. The FBI began investigating the series of bombings, dubbed "Mississippi Burning," and by June 21 of that year, local law enforcement officials had conspired with the KKK to beat and murder Schwerner, Chaney, and Goodman. Several of the conspirators were convicted, though four were never found.

Johnson says his faith was central to helping him withstand the trial, which led to the Voting Rights Act of 1965. "I believe that the first thing you must have is Jesus Christ in your life, not just in word, but in every aspect of your life, if you're going to do something in the atmosphere I had to do it in," Johnson says. "You have to be able to rise above your adversaries, and their meanness and their ways, and be an example so that you can help someone else. You must possess what you profess."

Johnson went on to march with Dr. Martin Luther King Jr. and subsequently led a march through Meridian after King was assassinated in 1968. During the 1970s, Johnson transitioned to more evangelistic crusades and pursuits. In 1984, he established the Black Leadership Conference of his denomination, the Church of the Nazarene, and in 2011, he was awarded the Miko Award for Civil Rights and Social Justice at the first annual National Civil Rights Conference. "You cannot let your feelings be your guide in whatever you're trying to do," Johnson says. "Because your adversaries will try you. They will try to get you to come down to where they are."