Depending on your experiences, church and temple probably bring to mind a variety of things for you—but we're betting that if you think on them for a bit, one of the things they'll bring to mind is community. Church and temple are not only places that people come to worship, after all, but also places that people come together, places that provide support in times of need and celebration in times of joy. And while nobody cares much about whether Margaret and her parents are religious back in New York, in New Jersey the opposite is true.
As soon as Margaret starts meeting people, it becomes clear that in her new town, joining a church or temple is the norm. In fact, it comes up the very first day she meets Nancy—and not as a question, but as an assumption. Nancy's mom says:
" […] Tell your mother we're making our car pools early this year. We'd be happy to help her arrange hers… especially Sunday school. That's always the biggest problem."
"I don't go to Sunday school."
Do you see how Nancy's mom doesn't ask if Margaret and her family go to church? She just assumes they do, and includes an offer of assistance with Sunday school rides in the middle of a string of invitations she's issuing to welcome Margaret and her mother to the neighborhood. In Nancy's mother's network, church seems to be a given—and that Margaret doesn't go immediately sets her and her family apart. Instead of representing connection and community—like places of worship typically do—in this book, they mark Margaret as different.
And it's not just adults who assume that everyone has a set religion and place they practice their beliefs. In the very first meeting of the PTS's, Margaret blows her fellow club members' minds when she explains that she is neither Christian nor Jewish. It comes up as they're trying to pick a regular day for club meetings:
"Okay, let's think up a good day," Gretchen said. "Tuesday and Thursday are out. I have to go to Hebrew school."
"Oh Gretchen!" Janie said. "You and that Hebrew school business. Can't you get out of it?"
"I'd love to," Gretchen explained. "But I've got to go one more year and then I'm through."
"What about you, Margaret? Do you go?" Janie asked me.
"You mean to Hebrew school?"
"No, I don't go," I said.
"Margaret doesn't even go to Sunday school. Isn't that right?" Nancy asked.
"Yes," I answered.
"How'd you arrange that?" Gretchen asked.
"I'm not any religion," I said.
"You're not!" Gretchen's mouth fell open.
"What are your parents?" Janie asked.
"Nothing," I said.
"How positively neat!" Gretchen said.
Then they all just looked at me and nobody said anything and I felt pretty silly. (5.50-65)
We learn a couple of key things in this little conversation between Margaret and her new BFFs. The first is that attending either temple or church is the norm amongst their social group, and so much so that it even seems possible none of them have ever met a kid who doesn't go to one or the other. Gretchen thinks Margaret must have worked some magic on her parents to get out of going (arranging something implies working to set it up), and when she learns that Margaret is religion-less, her mouth falls open, showing us how shocked she is by this news.
Again we see Margaret not quite fitting in with her new community. Each of her new friends has grown up with religion, and so while Margaret may have found a social group, she's still a little bit separate from them.
The other thing that this passage clues us into is the general lack of religious diversity in Margaret's new community. The only options ever presented to Margaret—or mentioned in the book—are Judaism or Christianity… which are pretty closely related to each other, and only two out of thousands of religious options.
This lets us know that Margaret's new town is rather homogenous (which is a fancy way of saying uniform). People here aren't used to religious diversity, so a girl whose connection to God is clearest in the comfort of her bedroom is definitely an odd duck—and because it's so easy to be a religious odd duck, we also get the sense that it's probably pretty easy not to fit in in other ways in this town.
So when Margaret concludes after her yearlong exploration of religion that she doesn't think she'll be picking a side any time soon (24.6), we are reminded that this is a girl with the gumption to follow her heart, no matter what everyone around her does. Church and temple may signify community for some, but Margaret's got her own thing going with God and she's in no rush to change that.