When Mayor Bill de Blasio came to East New York, Brooklyn, on Sunday to promote his transformative yet contentious development plan for the area, he could not have asked for a better setting than St. Rita’s Roman Catholic Church.

It was not simply the resplendent stained glass, or the eager flock of 700. The church also sits at the crossroads of the administration’s plan to transform blocks of rowhouses, auto body shops and vacant lots into a community filled with new classrooms, bike lanes, trees and, above all, lower-cost housing.

On one side of the church on Shepherd Avenue are tidy rows of brick and siding-clad houses. The city’s plan would largely preserve them, along with side streets throughout the area.

Toward the other side, on the corner of Atlantic Avenue, sits a single-story Medisys health clinic. Under the new rezoning, released in September, the clinic, as well as many buildings along Atlantic Avenue from Eastern Parkway to City Line Park, would quite likely be remade with 10- and 14-story apartment blocks.