When Avrohom begins travelling toward Eretz Cana'an, he takes with him "ha'nefesh asher asu b'charan," the people he made, which literally refers to slaves. Rashi adds that it can also refer to the people he converted (and homiletically created). In a previous discussion (here), we attempted to clarify the misunderstanding that the acceptance of all 613 mitzvos is not an integral and indispensable part of the gerus process; rather, accepting G-d and His Torah define the gerus. However, if Torah and mitzvos are so crucial to gerus, how could Avrohom "convert" anyone without the concept of Torah and mitzvos existing yet in the world?[The Brisker Rav (Parshas Bo) actually proves that gerus existed before Har Sinai from the commandments about a ger with korban pesach, which the Ramban understands as referring to the originalPesach in Mitzrayim before Matan Torah. Additionally, Pharaoh'sdaughter Batya found Moshe when she was going to the Nile River, and Chazal (Sotah 12b, see Rashi) interpret her "swim" as a tevilas gerus. He brings other proofs as well.]The P'ninim Mi'bei Midrasha suggests that there are two major components to gerus: becoming a part of the Jewish people, and accepting and performing the 613 mitzvos. Before Har Sinai, only the first part, entering the Jewish nation existed. [The fact that there was a concept of being a Yisrael before Har Sinai is evident from several sources, the earliest probably being the gemara in Kiddushin (18a), which refers to Esav as a Yisrael mumar.] He proves his idea from the words of the Ritva (Kesubos 11a), explaining the conversion process for the Jewish people at Har Sinai:
ותו דאילו זרע אברהם כבר נצטוו על המילה ולהכניסם מקטנותם בבריתו ואין זה אלא גמר גירות
The Jews at Har Sinai only needed to "complete" the conversion they began with having a bris milah.
Based on this, the P'ninim Mi'bei Midrasha suggests a possible explanation for a well-known Maharal. Regarding the concept of "ger she'nisgayer ki'katan she'nolad dami," a convert becomes like a new born child insofar as being permitted to previously forbidden relatives, there is a dispute whether or not this concept applied atHar Sinai. The Meshech Chochmah (Devarim 5:27), says that if G-d permitted the Jewish people to stay married to their wives ("shuvu lachem l'ohaleichem"), many of whom may have been relatives, then they must have been considered new people not halachically related to their biological relatives.The Maharal, however, says that at Har Sinai the Jews were not awarded the status of "katan she'nolad dami," as evident from their disappointment with the new rules. If Moshe found the Jewish people "bocheh l'mishpichosam," crying for their families, which Chazalunderstand as their frustrations over being forbidden to their families, they must have remained forbidden to family members. While several interpretations have been given for the Maharal, the P'ninim Mi'bei Midrasha suggests that since all of the Jewish nation were already Jews and by definition halfway along the gerusprocess, their finalizing the gerus by accepting the Torah at Har Sinaiwould not be enough to change their status to a katan she'nolad. Only a person entering the Jewish nation from the outside changes their status enough to change their halachic DNA.http://youngerlight.blogspot.com/2012/10/old-school-conversion.html
Old School Conversion