גמ׳... רבי אומר ככם כאבותיכם מה אבותיכם לא נכנסו לברית אלא במילה וטבילה והרצאת דם אף הם לא יכנסו לברית אלא במילה וטבילה והרצאת דמים ... אמר מר מה אבותיכם לא נכנסו לברית אלא כו' בשלמא מילה דכתיב (יהושע ה, ה) כי מולים היו כל העם היוצאים אי נמי מהכא (יחזקאל טז, ו) ואעבור עליך ואראך מתבוססת בדמיך ואומר לך בדמיך חיי וגו' הרצאת דמים דכתיב (שמות כד, ה) וישלח את נערי בני ישראל אלא טבילה מנלן דכתיב (שמות כד, ו) ויקח משה חצי הדם ויזרק על העם ואין הזאה בלא טבילה אלא מעתה האידנא דליכא קרבן לא נקבל גרים אמר רב אחא בר יעקב (במדבר טו, יד) וכי יגור אתכם גר אשר בתוככם וגו'
...§ Rabbi Yehuda HaNasi says: “As you are, so shall the stranger be” (Numbers 15:15), which means as your ancestors were: Just as your ancestors entered the covenant only through circumcision and immersion in a ritual bath and the sprinkling of blood on the altar, so too they may enter the covenant only through circumcision and immersion and the sprinkling of some blood, which requires at least a bird offering. ...The Master said: Just as your ancestors entered the covenant only through circumcision, immersion in a ritual bath, and the sprinkling of blood, converts must do the same. The Gemara objects: Granted, they underwent circumcision prior to entering the covenant, as it is written: “For all the nation that left Egypt was circumcised” (Joshua 5:5). Alternatively, it may be derived from here, a verse describing the redemption from Egypt: “And when I passed by you, and saw you wallowing in your blood, I said unto you: In your blood, live; and I said unto you: In your blood, live” (Ezekiel 16:6). The Sages interpret the double mention of blood in this verse as referring to the blood of the Paschal offering and the blood of circumcision. The Gemara continues: And granted as well, they entered the covenant through the sprinkling of blood, as it is written: “And he sent the young men of the children of Israel, and they sacrificed burnt offerings, and they sacrificed peace offerings” (Exodus 24:5). The Gemara asks: But from where do we derive that immersion in a ritual bath was also part of the process of entering the covenant? The Gemara answers: As it is written: “And Moses took half the blood…and sprinkled it on the people” (Exodus 24:6–8), and there is no sprinkling of sacrificial blood without immersion. The Gemara objects: If that is so, that these three rituals are required by Torah law for a convert to enter the congregation, then now, in our time, when there are no offerings, we not should have the ability to accept converts. In response, Rav Aḥa bar Ya’akov says that the verse states: “And if a stranger sojourn with you, or whosoever may be among you, throughout your generations” (Numbers 15:14). This teaches that converts may be accepted throughout the generations, even when there is no Temple and sacrificial offerings are therefore impossible.
Rabba said: There was an incident in the house of Rabbi Ḥiyya bar Rabbi, and as Rav Yosef teaches it, Rabbi Oshaya bar Rabbi was also present, and as Rav Safra teaches it, a third Sage, Rabbi Oshaya, son of Rabbi Ḥiyya, was also present, in which a convert came before him who was circumcised but had not immersed. He said to the convert: Remain here with us until tomorrow, and then we will immerse you. Rabba said: Learn from this incident three principles: Learn from it that a convert requires a court of three people to preside over the conversion, as Rav Safra taught that the case involved three Sages. And learn from it that one is not considered to be a convert until he has been both circumcised and immersed. And learn from it that the court may not immerse a convert at night, as they instructed him to remain there until the following day. The Gemara suggests: And let us say that one should also learn from it that we require a court of experts to preside over the conversion, as Rav Safra identified that three expert Sages were present. The Gemara rejects this: Perhaps they simply happened to be there, but in fact three laymen would suffice. Rabbi Ḥiyya bar Abba said that Rabbi Yoḥanan said: A convert requires a court of three to preside over conversion, because “judgment,” is written with regard to him, as the verse states: “And one judgment shall be both for you and for the convert that sojourns with you” (Numbers 15:16), and legal judgments require a court of three judges.
The Sages taught in a baraita: With regard to someone who came and said: I am a convert, one might have thought that we should accept him; therefore, the verse states: “And if a convert sojourns with you in your land, you shall not oppress him” (Leviticus 19:33). The emphasis on “with you” suggests that only someone who was already presumed by you to be a valid convert should be accepted as a convert. If he came and brought witnesses to his conversion with him, from where is it derived that he is to be accepted? It is from the beginning of that verse, which states: “And if a convert sojourns with you in your land.” I have derived only that a convert is accepted in Eretz Yisrael; from where do I derive that also outside of Eretz Yisrael he is to be accepted? The verse states “with you,” which indicates that in any place that he is with you, you should accept him. ... I have derived only that a convert is accepted in Eretz Yisrael; from where do I derive that also outside of Eretz Yisrael he is to be accepted? The verse states: “With you,” which indicates that in any place that he is with you, you should accept him. ...Even in Eretz Yisrael, the Jewish people should accept converts, as it could enter your mind to say that it is only for the sake of benefiting from the goodness of Eretz Yisrael, and not for the sake of Heaven, that they are converting, and therefore they should not be accepted. And it could also enter your mind to say that even nowadays, when God’s blessing has ceased and there is no longer the original goodness from which to benefit, one should still suspect their purity of motives because there are the gleanings, the forgotten sheaves, and the corners of fields, and the poor man’s tithe from which they would benefit by converting. Therefore, the verse teaches us that they are accepted even in Eretz Yisrael.