Messianic Jewish communities have a lot to celebrate on Shavu’ot—the giving of the Torah at Mount Sinai, the giving of the Spirit at Pentecost, and even the birthday and yahrzeit (anniversary of one’s death) of King David.

But one traditional Shavu’ot custom that has a less obvious connection with the day is the reading of the book of Ruth.

Why is the book of Ruth read on Shavu’ot?

There are a few superficial connections: The story about Ruth and Boaz happened around this time of year, and Ruth is the great-grandmother of King David. But when have we ever been known to sit around every year on our birthdays talking about our great-grandmothers? What’s really going on here?

To ask an even bigger question, why was this book written in the first place, and why was it included in the Bible?

The book of Ruth concludes with a genealogy tracing David’s ancestry back to Ruth. It’s almost as if this is the whole point of the book. Yet Ruth was from Moab; Moab and Israel were usually not on great terms—in fact, Moabites were forbidden to become part of the “assembly of the LORD,” according to Deuteronomy 23:3! Does this mean that David was not really Jewish—and that he shouldn’t have been able to become king?