Question: As a Moabite, why was Ruth allowed to convert to Judaism? at the time that Ruth's first husband died, had she already converted?
THE AISH RABBI REPLIES:
The Book of Rut indeed requires explanation. The story begins in the land of Moav, where a Jewish woman named Naomi lived with her two sons and their wives, Rut and Orpah. Rut was a Moavite princess who had converted before marrying Naomi's son. There was a question, however, about the validity of the conversion; perhaps Rut only converted because she wanted to marry a Jew.
That's why, when the two sons die, Naomi instructs Rut and Orpah to stay in Moav: "Go and return each of you to your mother's house." Naomi was fulfilling the directive to discourage potential converts.
When the women refused to depart, Naomi again tried persuasion: "Turn back my daughters. Why should you come with me?"
This prodding was strong enough to send Orpah packing. Rut, however, was persistent, and responded with one of the most famous speeches in the Bible: "Wherever you go, I will go. Wherever you lodge, I will lodge. Your people shall be my people, and your G-d my G-d. Where you die, I will die, and there I will be buried" (Rut 1:16-17).
With these words, it became clear that Rut's original conversion had been sincere, not just for the sake of marriage.
There's an additional reason why Rut's conversion was controversial. She was from the nation of Moav, and the Torah proclaims that because of their historic cruelty toward the Jewish people, a Moavite is not permitted to convert (Devarim. 23:4). However, upon closer inspection we see that the Torah was precise in writing the word "Moavite" in the masculine form, indicating that only Moavite males are forbidden to convert, but Moavites female are allowed to convert. This is alluded to by the fact that Rut's Hebrew name, when spelled backwards, means "dove," a kosher bird. This symbolizes that Rut was permitted to enter the Jewish people.
Sources: Talmud - Yevamot 77a, Midrash Ruth, and Zohar Chadash - Ruth 78a