After Passover, the second biblical pilgrimage feast is the first fruits festival, Shavuot, celebrated beginning this evening.
“And you shall celebrate the Feast of Weeks, that is, the first fruits of the wheat harvest, and the Feast of Ingathering at the turn of the year” (Exodus 34:22).
Traditionally on Shavuot, Jews eat of the seven species (wheat, barley, grapes, figs, pomegranates, olives and dates) which grow in abundance in the Land of milk and honey. Observant Jews stay awake all night on Shavuot studying the Torah because, according to tradition, thunder and lightning kept the children of Israel awake on the night Moses received the Law on Mount Sinai (see Ex. 20:18).
While the exact date of the passing down of the Torah (Exodus 19 and 20) is not specified in Scripture, Shavuot, the 3rd of Sivan, has been the traditional Jewish commemoration of receiving the Law.
The Book of Ruth is read because the Moabitess helped her mother-in-law Naomi at the “harvesting of the wheat.”