It was one of those magical moments the National Folk Festival has been known to inspire.

Shortly after jazz musician Mark Finks of Falmouth took out his banjo Sunday afternoon, a shirtless man joined in with a harmonica.

The two hadn’t played together before, but you’d never know it from hearing how the banjo, harmonica and Finks’ voice blended, lending a new twist to an old New Orleans-style spiritual.

The impromptu jam session, which occurred near the intersection of Front and Union streets, no doubt was one of many during the three-day event.

Though not on the official roster of festival performers, Finks has brought his banjo music to the National Folk Festival for two consecutive years as part of his street ministry.

A former educator in Christian day schools, Finks is sometimes misunderstood. He ran into some difficulties during last year’s festival because organizers and police believed he was a panhandler.

The city’s legal department recently reviewed the matter at the request of Finks’ attorney and determined that the jazz musician had a right to express his views in the public rights of way so long as he did not impede pedestrian or motor vehicle traffic.

Finks, who has performed and recorded with pioneer New Orleans musicians, is a recording artist on the GHB/Jazzology and Artesan record labels. A Yale graduate, he was featured in a reunion concert of Eli’s Chosen Six, a legendary Yale traditional jazz band featured in the Bert Stern documentary of the 1958 Newport Jazz Festival titled, “Jazz On a Summer’s Day.”

Now 56, Finks has been working to spread the gospel for 25 years, both through his music and as a Christian educator.

“I’m sort of a generic Christian,” he said. He described his ministry as nondenominational.

“The message is the gospel but the carrying medium is music,” Finks explained. “It encourages people who believe, and for opening the minds of those who don’t, it’s a gentle way to do it.”

Rather than preach hellfire and brimstone, Finks carries religious tracts for those who want to learn more about the gospel. He keeps his open banjo case at his feet for those who want to contribute to his ministry.

“It’s really come out of the heart and soul of America,” Finks said of traditional jazz. “And old New Orleans traditional hymns are part of the bedrock foundation of jazz. It doesn’t get much simpler than that.”

Finks says he measures his impact by the smiles on people’s faces and the numbers of passersby who hang around to listen to his music and his message.

He also said that people who want to know more about the gospel often seek him out in Portland’s Old Port district, where he frequently can be found strumming his banjo.