When he agreed to perform a one-man version of “A Christmas Carol” to help raise money for charity, Gerald Dickens thought that would be the end of it. “I said, ‘This will just be a one-off,’ ” said Dickens, 54, a British actor and the great-great-grandson of the beloved English novelist Charles Dickens. But that was 24 years ago, and the modern-day Dickens has made a career of immersing himself in his ancestor’s work and touring the United States and Great Britain. “I got to the end of that first performance and thought, ‘This is crazy not to carry on doing this,’ ” he said. On Monday, Dickens will bring his stage act to Portland, marking the first time in 149 years that a Dickens has traveled to Maine to perform “A Christmas Carol.” He will bring the beloved story of Ebenezer Scrooge and holiday redemption to the First Parish Church, a setting with deep ties to Dickens’ time and the author’s friend Henry Wadsworth Longfellow, who worshipped there with his family. “We thought it would be a wonderful venue, because it’s such a historic location and gives such a historic feel,” said Kate McBrien, the chief curator at the Maine Historical Society, which organized the performance. The show is bare and depends on few props, Dickens said.