'Amazing Grace': An Inside Look at the Musical

— -- It’s a song known to many -- and a story known to few.

"Amazing Grace" has been sung by pop artists, performed by public figures -- even presidents. Now, it has a Broadway debut in the musical "Amazing Grace," which chronicles the life of John Newton, writer of that beloved hymn.

“One of the most iconic songs in the Western world was the result of this life, this transformed life,” creator Christopher Smith told ABC News.

Smith, a former police officer, wrote the music and book for the musical after finding Newton’s autobiography on a library visit in 1997. He’s since worked tirelessly to bring the story of this slave-trader turned abolitionist to life.

“We love people that can look into themselves and can change and transform,” he said. “And that's what John Newton did and it's what compelled me.”

In the show’s most disturbing scene, a group of slaves, packed inside a crate, is brought onto the stage. Veteran Broadway actor Chuck Cooper, who plays Newton’s slave, said he had to mentally prepare for the role, telling ABC’s Ron Claiborne, “It has karmic weight, it has resonance, it has a power that is so much bigger than the moment.”

“It’s hard, it’s hard, it’s scary,” Cooper continued. “I can’t describe that, because to put myself in that place and to be that vulnerable, I was wary of that months before I got the part.”

The show’s debut comes just after President Obama’s emotional and poignant rendition of "Amazing Grace," part of his eulogy for a victim of the South Carolina church shooting in June. The national moment captivated the country -- and the cast of "Amazing Grace."

“It stopped us in our tracks, it really validated what it means about the human heart and what it means to forgive,” explained Smith. “And when the president sang that song, our hearts just opened up and we just felt -- there was no other song. What else would you sing? What else is there that truly captures the grace of those families in that moment?”

Audiences have also connected to the song, often standing to sing with the cast at the end of the show.

“This song is so powerful. this song transcends everything,” said Smith. “It may well be the most powerful song ever written.”