NEW YORK -- During his eulogy for the Rev. Clementa Pickney, one of nine worshipers killed at Emanuel AME Church in Charleston, S.C., a visibly moved President Barack Obama paused as he pondered mysteries of grief and forgiveness.

"Blinded by hatred," he said, the gunman could not comprehend the "power of God's grace. … Amazing grace. Amazing grace." The president then began singing: "Amazing grace! How sweet the sound, that saved a wretch like me! I once was lost, but now am found, was blind, but now I see."

The congregation joined in during that June 26 service, which was not a surprise since researchers say believers worldwide sing the Rev. John Newton's classic at least 10 million times a year.

But the president's solo had an unexpected impact in New York, where the cast of the Broadway musical "Amazing Grace" was doing preview performances before its July 16 opening in a tough town for a show about sin, repentance and salvation.

Some theater insiders, for example, had suggested changing the show's name.

"When Obama sang the song it was like heaven for us. If the president knew this song, that meant it was acceptable, that it wasn't just something for church people," said veteran playwright Arthur Giron, who wrote the musical's book -- dialogue and many lyrics -- along with self-taught composer Christopher Smith.

"You see, many Broadway people didn't know 'Amazing Grace,' let alone what the song was about. They obviously didn't know the story of the song and that was the whole point of our show."

The musical was based on the life story of Newton, a rebellious and profane young Englishman who was forced into the Navy, only to escape into the slave trade. Then, in 1748, Newton cried out to God for mercy during a sea storm, a conversion that led him to become a hymnist and Anglican pastor whose work inspired opponents of slavery. The highly personal hymn "Amazing Grace" was published in 1779.

Giron said it took six years to bring "Amazing Grace" to Broadway, including a successful run in Chicago beginning in the fall of 2014. The goal from the start was to earn a Broadway label and the production ran for 114 shows, after 24 preview performances, in the 1,232-seat Nederlander Theatre -- closing on Oct. 25.

Critics were skeptical, at best, with Variety offering this blunt judgment: "Ye of little faith will find it tough sledding." The New York Times did applaud the show's attempt to deal -- live on stage -- with the brutal realities of slavery.

While "Amazing Grace" drew enthusiastic interracial audiences, Playbill noted that it took in "only $332,663 out of a possible $1,097,840" during its best week.

Still, the Broadway cast recorded a cast album on Nov. 2 and producer Carolyn Rossi Copeland, while expressing disappointment at box-office totals, officially noted: "I look forward to bringing this story of hope and redemption to audiences around the country with our upcoming national tour."

Giron said the "Amazing Grace" team always knew it was facing a cultural dilemma: "How do you tell a spiritual, moral story about redemption in the commercial context of modern Broadway? … We knew that we may have created a product that will sell better in Middle America."

In addition to its religious content, "Amazing Grace" faced questions about the wisdom of offering an epic historical production -- 91 people worked backstage with costumes, props and effects -- in a Broadway marketplace known for flashy shows recreating Hollywood hits.

"There was a cynical feeling out there that Christians would not show up en masse for anything on Broadway. … We knew we were trying to bring a new audience to Broadway," said Giron.

While the show's success on the Great White Way may have been limited, he said, it was thrilling -- night after night -- to see a very different kind of audience on its feet singing the final number with the cast.

"We knew that the audience would respond when, at the end, we finally got to the song itself. We knew there would be tears," said Giron. "But we had earned that moment. We told the story. We told how this man went on that journey to redemption and ended up writing that song. That was the point."