Why does Rabbinic Judaism tend to be reluctant to receive converts? The Jews have always been a nation that welcomes newcomers, however Rabbinic Judaism does not missionize and Orthodox Judaism typically demands a prolonged waiting period to show sustained ritual observance before someone is converted, in the Diaspora typically three years. What is the historical explanation for this? The halakhic rules for conversion only emerged with halakha (rabbinic religious law) which itself is a product of the Babylonian Talmud which for several centuries was oral only until it was codified in the 6th century CE.
The basic reason why rabbis tend to be skeptical of potential converts is that historically and in the present converts tended to not remain faithful to rabbinically Jewish religious practice which is a demanding and challenging religion to be part of. The fear among Orthodox rabbis is that someone will convert, become a practicing Orthodox Jew, marry a born Orthodox Jew and then suddenly cease to be observant in causing any children in marriage to not remain religious either. Another fear among Orthodox rabbis is that lenient conversion standards will lead Orthodox Jews to date non-Jews who will convert, marry Orthodox Jews and then will not remain observant, thus leading to assimilation in the Orthodox Jewish community itself. There has however, as evidenced in the Talmud always been a wide spectrum of rabbinical opinions on conversions from the most lenient to the most stringent. Historically, rabbinic attitudes towards potential converts varied from in some periods performing mass conversions to in yet other periods having very stringent criteria and making it very difficult for non-Jews to be accepted for conversion to Judaism.
Since before the inception of the State of Israel, Orthodox Judaism has had a monopoly on state-funded and state-recognized Jewish religious services, including conversions to Judaism. This is the continuation of the Ottoman Millet (religious nationality) system which granted religious autonomy to recognized religious communities with their religious courts to adjudicate matters of family law. The millet system was retained in the British mandate in the land of Israel and inherited by the secular State of Israel as founded in 1948. Orthodox Judaism generally does not recognize conversions performed by non-Orthodox denominations of Judaism with the exception of those converts to Conservative Judaism who become religiously observant and regularly frequent Orthodox synagogues and who are often recognized as Jewish by Orthodox rabbis.
During most of the 20th century it was the rule that any person converted by an Orthodox rabbi was recognized as Jewish by Orthodox Judaism. However in the past three decades has there been a process of increasingly not recognizing conversions performed by many Orthodox rabbis, usually due to those individual rabbis being perceived as halakhically lenient on conversions. When an Orthodox rabbi is unrecognized as a rabbi are all conversions he has historically performed deemed invalid irrespective of the level of observance of the individual converts and this also affects matrilineal offspring of such converts. This happened to modern Orthodox US rabbi Haskel Lockstein who converted Ivanka Trump to Judaism in 2009. One of his converts did later become unrecognized by a rabbinical court in Israel and thus were Lockstein and all his converts, including Ivanka Trump unrecognized and the converts deemed non-Jewish. This has affected Jared Kushner’s and Ivanka Trump’s two sons who thus became unrecognized as Jewish. Jared Kushner’s brother Josh Kushner also dated a non-Jewish woman who subsequently converted to Orthodox Judaism before marrying him. The Kushner family are modern Orthodox Jews and their two sons dating non-Jews was precisely the kind of scenario that Orthodox rabbis try to prevent by making it difficult to convert to Judaism.
Since the late 1980s period of the Glasnost in the former Soviet Union have half a million descendants of Jews along with one million Jews immigrated to Israel from Russia, Ukraine and other former Soviet republics. The Israeli Law of Return grants the right to immigrate to Israel not only to Jews but to children of Jews, grandchildren of Jews and their spouses and dependent children. Until the great wave of immigration from the former Soviet Union, conversion standards by the Israeli state Chief Rabbinate were highly lenient as virtually all relatives of Jews who immigrated to Israel were almost automatically converted without checking individual observance. Until then were conversions performed by municipal rabbis, but the influential Haredi (Ultra-Orthodox) political parties in the Knesset changed the rules and centralized conversions under the authority of the Chief Rabbinate which had become increasingly dominated by Haredi rabbis who made it more difficult to convert to Judaism. As a result, most of the half a million descendants of Jews in Israel never converted to Judaism.
The current Israeli government does not include any Haredi political parties and the prime minister is Naftali Bennett, leader of the liberal Orthodox Yamina party. The government seeks to return to the previous system of municipal rabbis performing conversions with the important addition of actively persuading Israeli descendants of Jews to convert to Judaism.
Haredi rabbis once recognized the conversions performed by the Israeli Chief Rabbinate but no longer do so. Despite not recognizing conversions of the Chief Rabbinate, Haredi political parties are actively trying to prevent the more lenient municipal conversion process from being reinstated. They have been joined by many Hardal (Haredi-leaning Modern Orthodox) rabbis who also oppose return to the previous municipal system of conversion.
What is behind this opposition? The modern Orthodox rabbis promoting return to the municipal conversion system seek to integrate Israeli descendants of Jews in the Jewish nation while preventing intermarriage. The Haredi rabbis do not believe that non-Haredi Israeli Jews will remain Jewish forever but will eventually after a number of generations become non-Jews just like most Palestinians are descended from Jews who became non-Jews over the course of history by leaving Judaism. Haredi rabbis encourage adherents to give birth to many children in the hope of eventually by demographic means taking over the Israeli state and turning it into a Jewish theocracy. Haredi rabbis therefore have a different strategy for keeping Israel Jewish than most Modern Orthodox rabbis.
Since most non-Jewish Israelis of Jewish ancestry have no intention of becoming Orthodox Jews after converting to Judaism will the effect of the conversion reform on Orthodox Judaism be minimal indeed. However, Haredi rabbis fear that Modern Orthodox Jews will marry converts and their descendants and thus deepen the rift in Orthodox Judaism as to who is a Jew. This problem exists already in the United States where Ivanka Trump and her sons and a large proportion of Orthodox converts and their descendants are not recognized as Jewish by the Chief Rabbinate in Israel. This is caused entirely by the novel Haredi practice of unrecognizing many Modern Orthodox rabbis, yet the Haredi rabbis blame the Modern Orthodox rabbis for being too lenient on conversions as in their view conversion to Judaism is meaningless unless the convert becomes an Orthodox Jew for his entire remaining life.
Both Modern Orthodox rabbis and Haredi rabbis are concerned with the survival of the Jewish people yet employ different strategies towards this end. For Modern Orthodox rabbis, protecting the Jewish character of Israel is essential to their strategy for Jewish survival while for Haredi rabbis this will be ensured by the high Haredi fertility rate and insulating Haredi Jews from influences of modernity. Non-Haredi Jews will according to this view not remain Jewish over the course of generations and therefore according to this reasoning it is meaningless to convert non-Jewish Israeli descendants of Jews who do not intend to become observant Orthodox Jews.