Yevamot 23 - 29
Our Rabbis taught in a beraita: “Converts to Judaism will not be accepted in the days of the Mashiach; similarly, converts were not accepted in the days of King David or in the days of King Solomon.”
The basis for this teaching is presented in the gemara by Rabbi Elazar, based on his understanding of a verse in the Prophet Yishayahu 54:15. The most logical reasoning for not accepting converts in times of Israel’s glory — such as in the days of Mashiach — is a concern that the person is converting with an ulterior motive to join the Jewish People only because they have power and authority, and would not be converting as a “righteous convert” (Rashi).
Tosefot asks how, in light of our gemara, are we to understand the statement elsewhere in our masechta (79a) that 150,000 people converted in the days of King David? Tosefot answers that these people “converted” to Jewish practices “by themselves”. They called themselves Jews although they were not formally accepted. This is similar, says Tosefot, to many who “converted by themselves” when the Jewish People rose to a position of strength and great influence in the time of Mordechai and Esther after the miracle of Purim.
- Yevamot 24b
Rava said, “A person is related to himself and cannot establish himself (through his testimony) as a rasha (evil person who is obligated).”
Relatives cannot testify for or against one another as we learn elsewhere in Shas, and no one is a closer relative than a person to himself! However, this lack of ability to cause self-incrimination only applies to physical punishments, such as receiving lashes or capital punishment by the Beit Din religious court, or to monetary penalties that only the courts can impose, or for making the person unfit to be a witness. However, if one admits in his “testimony” that he owes another person money for some reason, his word is accepted by the Beit Din (as learned from a verse specific to this situation of admission of monetary obligation), and the person is found “guilty” to pay the debt based on his own words. (Rashi and Tosefot)
- Yevamot 25b