Why do we read the Book of Ruth on Shavuot?
AISH RABBI REPLIES: One reason is that Rut is the
ancestor of King David, who was born on Shavuot, and died on Shavuot.
The other reason we read about Rut is because on the first Shavuot, when the
Torah was given at Mount Sinai, each Israelite essentially became a "Jew by
Choice." That's why the Talmud and Code of Jewish Law use the Sinai experience
as a basis for determining the requirements of all future converts:
1) Mikveh - All converts must immerse in a Mikveh (ritual bath) -- as the
Israelites did at Mount Sinai (Shemot 19:14, 24:8).
2) Milah - Male converts must undergo circumcision -- as the Israelites did
before leaving Egypt (Shemot 12:48; Yehoshua 5:5).
3) Mitzvot - All converts must accept to observe all 613 mitzvot of the Torah --
as the Israelites did at Mount Sinai (Shemot 24:3).
Interestingly, the Torah intimates that the souls of eventual converts were also
present at Sinai, as the verse says: "I am making
[the covenant] both with those here today before Hashem our G-d, and also with
those not here today." (Devarim 29:13)