REVERTS, ADMISSION OF:
The rabbinical law takes notice of apostates ("mumarim"; the popular name "meshummadim" is of somewhat modern origin); and apostasy is treated as the sum of all iniquities. But the person guilty of apostasy does not cease to be an Israelite. He may repent and return to his former good standing; "for there is a place where the repentant sinner stands, which the perfectly righteous can not reach."
On this subject Maimonides ("Yad," Teshubah, iii.) is quite explicit. He enumerates twenty-four classes of grave sinners, among them those who deny the divine source of the Torah; those who, like Zadok (the supposed first head of the Sadducees) and Boethus, deny the oral law; those who, like the Christian and the Moslem, assert that God has abrogated the Torah and has established another religion; and finally those who act as informers against Israelites and deliver them over to the Gentiles for spoliation and death. But he concludes with the words: "Any one of all these, should he die without repentance, has no share in the world to come; but if he has turned away from his wickedness, and dies while repentant, then he is among the inheritors of the world to come; for nothing can stand before the force of repentance. Even one who has for all his days denied the fundamentals, but turns at the last, has his share in the world to come." He quotes the Scripture (Isa. lvii. 19, Hebr.): "Peace, peace to the near and to the far, saith the Lord; and I will heal him." "Hence," he says, "we should receive all the wicked, even apostates and the like, who turn back in repentance, whether openly or secretly"; quoting Jer. iii. 14, Hebr.: "Return, return, ye back-sliding sons."
The question whether an apostate returning secretly to the old faith is to be received, dates back to a dispute among the early sages, those of the generation of R. Meïr ('Ab. Zarah 7a, b; Bek. 31a). Meïr would not receive them back at all; another disputant, only upon a public recantation; while two others held that even he who returns in secret should be received; and this most liberal view is approved by the amoraim who pass upon this dispute in the two Talmudic passages of the Talmud which have been cited above.
The manner of accepting the penitent back into the fold is not discussed by Maimonides, nor by the Shulḥan 'Aruk. The reason is plain: both Christians and Mohammedans, especially the former, dealt very harshly with relapse into Judaism, punishing it with death as a matter of course. Hence a secret return was generally deemed most prudent; and the reception of the "revert" could not be very formal.