Houses of worship struggle with fear of Delta’s rise within their congregations.

The weekly rhythms of Catholic life have started to return at Our Lady of Lourdes in Harlem. The pews are packed on Sunday mornings, prayer groups meet after work and the collection plate is almost as full as it was before the coronavirus pandemic began.

But parishioners are starting to worry about the virus again.

“For a little while, everyone felt more free, not using masks and things like that,” said the Rev. Gilberto Ángel-Neri, the pastor. “But now that we hear all the news about the Delta variant, everyone is using masks again.”

The progress made at Father Ángel-Neri’s church, and at houses of worship across New York City, may be threatened by a rise in virus cases in the past month and by an uneven patchwork of rules governing vaccination.

New rules to curb the spread of the virus’s more contagious Delta variant require New Yorkers to show proof of vaccination to participate in many indoor activities, including sitting inside restaurants or bars, going to a gym or nightclub and visiting a museum or zoo. But they do not apply to religious services, and most churches in the city do not require worshipers to be vaccinated, though approaches vary from place to place.

“Faith is a light to help you navigate through uncertainty and darkness, but what a lot of people have been grappling with is what do you do when church itself becomes a place of anxiety,” said John Gehring, the Catholic program director at the advocacy group Faith in Public Life.