The author observes that traditional religious organizations (a.k.a. "churches") have historically been the source of community in Western culture, then suggests that secular organizations could compete with them.
I'm intrigued that he suggests secular communities should "put fellowship first" and "appeal to all kinds of people" in order to do so, when the traditional religious communities that he says succeed don't set out to do those things.
In a functional Christian church (and granted, many US churches are not), the community's shared goal is to love and serve God and the people around them.
The community, and any appeal it has, are side effects.
This shared goal comes straight from the Bible. If you read the whole thing, you'll find the theme appears throughout, but Jesus espouses it very clearly in Matthew: https://www.biblegateway.com/passage/?search=Matthew%2022:36...
As a Christian who grew up in the church, and has watched various Christian communities function (and sometimes dysfunction), I think this belief, at the very core of Christianity, is exactly what makes many churches wonderful communities.
Each member of the church believes that the crafter of particle physics, the shaper of Mount Everest, the painter of the auroras, loves them so intensely that he took on human form and died to save them from the worst decisions they have made, the betrayals that devastated their friends, family, themselves, and him.
You may think that belief is ludicrous, and that we are naive, irrational fools for holding it.
Even so, it should be clear that those who believe it would feel compelled to follow that example, as much as they can. Caring for others that well is nigh-impossible, but it's the unattainable standard a church strives for.
Many churches have long forgotten what they once believed. Even when it's remembered, humans remain frail as ever. It is not easy to put others before yourself even when you like them, let alone when they belittle and insult you.
When it works, though, it's amazing to see.
I think that's why few secular communities or institutions have outlasted the Christian church. Right or wrong, the Christian vision has caring for others as an essential imperative.
That seems to me to be the very essence of a community.
I may be blinded by my bias, but I don't see how an explicitly secular organization could have as rich a community.
It cannot point to the perfect exemplar of their ideals and say "This is how you should strive to be." It cannot say "The earth and its works will be unmade and remade, but the communities you forge now will live into eternity."
"If we don't make better communities, we'll be sadder before we die" just doesn't seem as compelling.