Why do Jews read the book of Ruth on Shavuot?

Because the story of Ruth is what the Shavuot legislation looks like in practice.

The feast is commanded in Leviticus 23:15–22. The final verse of that unit is an abrupt command about gleaning:

"And when you reap the harvest of your land, you shall not complete the edge of your field in your reaping, and the gleaning of your harvest you shall not gather; for the poor and the sojourner (le-ani ve-la-ger) you shall leave them. I am the LORD your God." — Leviticus 23:22

The command itself is a repetition — the same rule is given in Leviticus 19:9–10. What's striking is the placement. The gleaning law is inserted into the Feast of Weeks legislation, sandwiched between the leavened loaves and the Feast of Trumpets. The Torah ties this harvest-feast to leaving enough in the field for the outsider.

Now open Ruth 2. Ruth is a Moabite — a sojourner, a ger (Ruth 2:10). She goes out to glean in Boaz's field — va-telaqqet, the exact verb from the gleaning law (Ruth 2:2–3). Boaz's command to his young men (Ruth 2:15–16) goes beyond the legal minimum: not just leave gleanings, but drop handfuls on purpose for her to find. The narrative timeline matches too: Ruth 2:23 locates the events in the barley harvest running into the wheat harvest — the seven-week window Leviticus 23:15 defines as the count from Passover to Shavuot.

The fit is textual. The season is Shavuot's season. The category of person is exactly who Leviticus 23:22 commands generosity toward. The legal vocabulary is shared. And Deuteronomy 16:11 — the parallel Shavuot command — explicitly names "the sojourner and the orphan and the widow" as required guests at the rejoicing.

That said, it is important to be honest: the canonical text of Ruth doesn't name Shavuot. The book doesn't say "this happened at the Feast of Weeks." The liturgical pairing — reading Ruth on Shavuot in the synagogue — is traditional, preserved in Jewish custom, not commanded in Scripture. Christians haven't universally adopted it. But it's not arbitrary. The tradition noticed what the Torah did when it placed Leviticus 23:22 inside the festival legislation, and the community that reads Scripture liturgically paired the narrative that enacts the law with the feast that contains the law.

There's one more connection worth seeing. Ruth ends with a genealogy: Obed, Jesse, David (Ruth 4:17, 22). The gleaning of a Moabite sojourner on the threshing floor of a landowner who obeys Leviticus 23:22 produces the line from which King David — and eventually the Messiah (Matt 1:5) — is born. The feast that legislates radical inclusion produces, in narrative, a king whose ancestry is precisely the kind of outsider the law was written to shelter.

For the broader frame of how the Shavuot legislation's inclusion theme reaches all the way to Acts 2's "Jews from every nation under heaven," read the full study: Count Fifty Days.