Ask the Rov: What are the halachic requirements for a non-Jew to convert?
By Rabbi Chaim Hillel Raskin – Rov of Anash in Petach Tikvah
When a ger enters the covenant with Hashem, he must follow the same process as the Bnei Yisroel did at Har Sinai, including: milah (for men), immersion in a mikva, and offering a korban olah.1 Today that we don’t have a Beis Hamikdosh and cannot bring a korban, the geirus is complete without it. Yet, when Moshiach comes, the ger will bring a special korban for his geirus.2
The essence of geirus is of course that the ger accepts to live as a Yid and observe the mitzvos (kabolas hamitzvos).3 Thus, before performing the process, he must learn relevant mitzvos and accept them all.4 If he accepts the mitzvos without properly knowing them, his geirus is nonetheless valid.5
If a non-Jew goes through the technical steps of geirus but doesn’t accept the mitzvos, the geirus doesn’t begin.6 Even if the potential ger says that he accepts all mitzvos, but we have knowledge that he doesn’t intend to observe them, his “acceptance” is meaningless, and his geirus is invalid.7
In 5730 (1970), the government of Eretz Yisrael amended their Law of Return’s definition of a Jew and omitted the requirement that conversion be according to halacha. In the years that followed, many non-Jews immigrated to Eretz Yisroel and “converted.” To become citizens, they followed the geirus protocol despite having no intention of observing the Torah. Throughout the ‘Mihu Yehudi’ campaign, the Rebbe spoke passionately about this and emphasized that this was a farce and completely invalid.8
If the ger accepts all mitzvos except one, his geirus is likewise invalid. In this case, some say that if he truly believes in that mitzva as well, and he only intends to transgress due to temptation, his geirus is still valid.9 However, others disagree and contend that acceptance of a mitzva with plans to transgress it isn’t considered “accepting” at all and is meaningless.10 If he denies the existence of that mitzva or if he is not sincere about observing basic halachos (Shabbos, kashrus etc.), all agree that he cannot be accepted.
Once a ger genuinely and wholeheartedly accepted all mitzvos and was nisgayer according to halacha, then, if for whatever reason, he relaxes his observance, he remains a full-fledged yid and his geirus cannot be undone.
See Sources (open PDF)
From The Weekly Farbrengen by Merkaz Anash