In the synagogue, it is customary to read the book of Ruth because the story of Ruth embracing Judaism and the description of the scene of harvesting are apt for the festival of the Law and of the harvest. Another reason given is that King David, a descendant of Ruth, died on Pentecost. The Book of Ruth is a book in the Hebrew Bible known to Jews as the Tanakh and to Christians as the Old Testament. It recounts the story of the fidelity of a Moabite widow (Ruth) to her widowed mother-in-law (Naomi). Ruth adopts the faith and land of the Jews during the harvest season in Bethlehem. Ruth's gentle and considerate behavior towards her widowed mother-in-law, Naomi, attracts the attention of Boaz, the leader of the generation, who eventually marries her. The child born of their union is Oved, the grandfather of David. The outcome of Boaz and Ruth's union is a testimony of their personal greatness as well as the magnitude of the reward for deeds of kindness and the degree of recognition owed to a righteous convert for her unbounded piety.
Among Biblical figures, Ruth, the Moabitess, is unique in that there is no criticism of her in Jewish sources. Although others were as great or greater than Ruth, their shortcomings are highlighted by the sages. Ruth, however - the epitome of modesty, idealism, and loyalty - is portrayed as being faultless. Therefore Ruth fittingly serves as the Shavuot inspiration.