But the artist, a lover of music and Yiddish theater, added personal touches: The work shows musical instruments, dismaying some in the congregation, according to the archives. The upper part of the mural that rose above the ark survives; the lower half and the adornment of the ceiling having been lost over the years, after the building entered private hands.

In 1939, Chai Adam merged with Congregation Ohavi Zedek, and the mural later became a peculiar backdrop for the stores that later filled the space.

“It was kind of an intriguing oddity that was surrounded, as I recall in youth, by carpets and business and things of the sort,” said Jeffrey Potash, 60, who is also an archivist at Ohavi Zedek and who, like Mr. Goldberg, grew up here, noticing the mural. “So I never gave it much thought.”

But Mr. Goldberg’s intuition told him the mural was worth saving. When the building was to be converted into apartments in 1986, he tried in vain to find an institution that would take the mural. He made archival photos and had the mural hidden behind a false wall in the hope of eventually preserving it. At the time, Mr. Goldberg said, “There was really very little scholarly work that had been done on the lost painted synagogues. We couldn’t even determine what we had then.”

Image The painter, Ben Zion Black, right, with his wife.

For nearly 25 years, he says, tenants filled the apartment with no idea it was there. But it gnawed at Mr. Goldberg, who had a segment of the wall opened and resealed in 2010, and then began exploring his options to preserve the mural.

When the building was sold again, he approached its new owner, Steven Offenhartz, who was not himself sure what was behind the wall.