“I got this idea from the Baptist Church,” Ferrer told me, with a smile suggesting she appreciated the irony of borrowing from the missionary playbook. “They’re helping the community and, while helping, they’re also spreading the gospel. So as humanists, if they can do it, why can’t we?”

The Philippines has a population of 98 million and is one of the most deeply religious countries in the world. More than 80 percent of Filipinos self-identify as Catholic, with most of the rest belonging to a variety of other Christian denominations, according to the 2015 Philippine Statistical Yearbook. A small percentage is Muslim. Less than 0.1 percent of the population say they have “no religion.”

HAPI volunteers believe that challenging religion is a necessary prerequisite for developing Filipino society and ending its stark economic inequality.

“Advancement comes through science, technology, and social justice,” Ferrer said. “The country has a lot of potential—people just need to change their minds. You can't rely on a deity to get yourself out of poverty, you have to do it yourself.”

While she runs the classes, Ferrer’s colleague, Jamie Del Rosario Martinez, runs the food program, dishing out meat stew and rice to the children alongside young volunteers who have joined the mission.

Martinez lives with her husband and in-laws in the slum. To get out of the blistering heat, she invited Ferrer and me into her home. Although she is a nonbeliever, her family members are devout Catholics and their walls are plastered with crucifixes and images of Jesus Christ. A three-foot high statue of the Virgin Mary stood on the table next to the couch.

Martinez told me she didn’t want to air her views in front of her sister-in-law. Her fellow volunteer, however, was happy to keep talking.

“I read the Bible and every time I read it I felt so guilty,” Ferrer said. “Everything that you do is a sin.” She told me her parents were enthusiastic Baptists and that her father was “the type of man who liked talking about the apocalypse. It really scared me to death.”

Between the ages of eight and 10, Ferrer went to an Accelerated Christian Education school. After qualifying as a teacher herself, she taught at a Christian school run by her mother.

“I felt uneasy,” she said. “There was a pastor that would regularly come to school to show very young children in kindergarten films about hell. I believe that is one of the reasons why people stay in that religion, because of the fear of going to hell.”

It wasn’t a fear Ferrer found easy to overcome. Despite all her doubts, she didn’t give up religion until last year, at the age of 29. Her decision to “come out” as an atheist devastated her mother. “I am the only girl in the family,” Ferrer explained. “It really hurts her that I have ended up like this.”