When writing an inspirational biography to an LDS audience, do you think it's best to use serial commas?
A serial comma is when a comma is used in a series, for example:
I put caramel syrup, hot fudge, and whipped cream on my ice cream sundae.
The red one in front of the "and" is the one being asked about. I think. At least, whether or not to use this comma in a series is usually what people are asking about. Here's the sentence without it:
I put caramel syrup, hot fudge and whipped cream on my ice cream sundae.
Either is correct, or rather, an argument can be made either for or against it. The use of this comma goes in and out of style, and different editors/publishers will have differing opinions. Most style guides will say to use it. Newspapers often do not.
You can read about it here and here and here.
The most important thing to remember about this comma is to pick one way of doing it and stick to it.
And by the way, it doesn't really matter what you're writing—biography, fiction, poetry—or who your audience—LDS or not, children or adult—although generally, non-fiction and more literary works use it, while more casual works often do not.
I'd check a couple of top sellers by established publishers in your genre (or the publisher you're planning to submit to), see what their style is, and do that.
And no, it's not a big enough deal for you to do it both ways and send one version to one publisher and the other version to another. Just do it one way, CONSISTENTLY—and they'll tell you if they want it done the other way.