The point is that churches attract people who think they are doing good, and each church attracts local people. So you have a group of people who like being go

The point is that churches attract people who think they are doing good, and each church attracts local people. So you have a group of people who like being good to other people, are local, and some subset of that also enjoys activities centered on the church. (The rest just show up for services and then go home.) This is a group of local people with a common cause, and that makes a good place to meet friends. If you're already religious, then you can easily go to church, join the activities there, and make friends.