Unlike Judaism, Islam makes it very easy for a non-Muslim to become a Muslim. Although many Jews (like Christians) think Islam was spread by the sword, that is not correct. Indonesia has the largest population of Muslims in the world and was never overrun by a Muslim army.
The truth is that rabbinic law becomes overly concerned that some converts might become unobservant of some Mitsvot (as many Jews by birth are) and made it very hard to convert to Orthodox Judaism. Thus, although the Jews of Madinah did have large numbers of converts among them, they did not take advantage of the chance they had to convert the majority of the city’s pagan population to Judaism, the religion of Abraham and Moses.
Indeed, they mostly pushed interested Arabs away and left the field open for Prophet Muhammad. An Islamic Hadith narration provides us with one example.
Zaid Ibn ‘Amr Ibn Nufail stated that the tribe of Prophet Muhammad, the Quraish, were all polytheists prior to the revelation of the Qur’an to Prophet Muhammad: “Asmā bint Abu Bakr said: I saw Zaid Ibn ‘Amr Ibn Nufail standing with his back against the Ka’bah and saying, “O people of Quraish! By Allāh, none amongst you is on the religion of Abraham except me.” (Reported by Al-Bukhārī, no. 3828)
The same Zaid Ibn ‘Amr Ibn Nufail went to Syria, inquiring about a true religion to follow. He met a Jewish religious scholar and asked him about their religion. Zaid said, “I intend to embrace your religion, so tell me something about it.” The Jew said, “You cannot embrace our religion unless you receive your share of Allah’s anger.”
Zaid said, “I do not run except away from Allah’s Anger, and I will never bear a bit of it if I have the ability to avoid it. Can you tell me of some other religion?” He said, “I do not know any other religion except Hanīf (Abrahamic monotheism).” Zaid enquired, “What is Hanīf?” The Jew said, “Hanīf (monotheism) is the religion of Prophet Abraham who was neither a Jew nor a Christian, and he used to worship none but Allah alone.”
This Hadith correctly states that rabbinic Judaism tries to discourage non-Jews from converting to Judaism because of Christian anti-Semitism. “Our Rabbis taught: If at the present time a man desires to become a proselyte, he is to be addressed as follows: “What reason have you for desiring to become a proselyte; do you not know that Israel at the present time is persecuted and oppressed, despised, harassed and overcome by afflictions?”
“If he replies, “I know and yet am unworthy,” he is accepted forthwith, and is given instruction in some of the minor and some of the major commandments; and several more stringent commandments. And as he is informed of the punishment for the transgression of the commandments, so is he informed of the reward granted for their fulfillment. He is not, however, to be persuaded or dissuaded too much.
“If he accepted, he is circumcised forthwith. As soon as he is healed arrangements are made for his immediate ablution, when two learned men must stand by his side and acquaint him with some of the minor commandments and with some of the major ones. When he comes up after his ablution he is deemed to be an Israelite in all respects.” (Talmud Yevamot 47a)
Apparently, therefore, it is the task of the Jewish court about to accept the proselyte to inform him of the difficulties of Jewish destiny as well as of the particulars of some of the commandments. Nevertheless, the great legal scholar Rabbi Moses Maimonides, who lived his whole life among Muslims, and expresses the initial necessity of investigating the would-be convert to ascertain his or her sincerity as well as of informing the would-be convert of the substance of the yoke of Torah (Mishneh Torah, Hilkhot Issurei Biah 13:14-15) concludes:
“A proselyte, after whom the Bet Din did not investigate or to whom they did not inform the particulars of the commandments and their punishments, but who was circumcised and ritually immersed before three common Judges, is considered a convert. And even if they discover that it was for some ulterior motive that he converted, since he was circumcised and ritually immersed he has left the category of Gentile . . . And even if he returns (to his former ways) and serves idols he is considered an apostate Jew whose marriage is a marriage. (ibid, 17).
At least according to Rabbi Moses Maimonides, conversion to Judaism requires only the ritual of circumcision and the ritual of immersion which takes effect even without the judges having informed the would-be proselyte of all the details of the rabbinic commandments. This is the basis for the ruling of Rav Uziel, and might lead us to believe that acceptance of all the commandments is a desirable but not a necessary constituent of conversion.
In reality, discussions among Orthodox Rabbis are more about the rules that are used to keep potential converts out than they are about the desirability of welcoming converts in.
The Hadith then continues: “Then Zaid left the Jew and met a Christian scholar and asked him what he asked the Jewish scholar. The Christian said, “You cannot embrace our religion unless you receive a portion of Allah’s curse (that every human is guilty of Adam’s original sin and that the death of Prophet Jesus was a vicarious atonement for your own personal sins).”
Zaid replied, “I do not run except from Allah’s curse, and I will never bear any of Allah’s curse or His anger if I have the power to avoid them. Will you tell me of some other religion?” The Christian replied, “I do not know any other religion except Hanīf.” Zaid enquired, “What is Hanīf?” He replied, “Hanīf (monotheism) is the religion of Prophet Abraham who was neither a Jew nor a Christian and he used to worship none except Allah alone.”
When Zaid heard their statements about the religion of Abraham, he left that place, and when he came out, he raised both his hands to the skies and said, “O Allah! I make You my witness that I am on the religion of Abraham.” (Reported by Al-Bukhārī, no. 3827)