A sociologist of religion describes what she found when studying “secular congregations”:

Many features of atheist churches in the U.S. are directly borrowed from religious organizations. At Sunday Assembly, where I spent three years doing research, services include collective singing, reading inspirational texts, silent reflection and collecting donations. They center around a central lecture given by a member of the congregation or a member of the larger local community. I attended one service where an astronomer gave a talk about the New Horizons spacecraft’s mission to Pluto. At another service, a member of a local community garden organization talked about building community through her community garden program.
Atheist church organizers I met told me that they intentionally borrow the structure of a church because they see it as a good model for building effective rituals and communities. More generally, the structure of a “congregation” is popular and familiar to most attendees.
However, there are key differences. Sunday Assembly has no hierarchical structure, and there is no pastor or minister, meaning that decisions are made by the community. Attendees share duties for running the services and finding speakers and readings.
The other key difference is the complete lack of reference to the supernatural. Lectures and rituals I have encountered at atheist church services are centered around affirming atheistic beliefs, celebrating science, cultivating experiences of awe and wonder for nature, and creating communities of support.
Communities and rituals are pretty important to human beings. So are religious beliefs and practices.
I wonder how much the decline of civic organizations and engagement also contributes to these kinds of congregations. Yes, there is a decline in religiosity – but there is also less engagement with civic groups and community life.
Additionally, will the same sorts of issues that religious congregations face – disagreements and fracturing, abuses of power, difficulties acquiring resources – be ones that secular congregations encounter?