Halakhah su Levitico 18:13

1. Rambam records the prohibition against residence in Egypt both in Sefer ha-mizvot, negative commandment no. 46, and in Mishneh Torah, Hilkhot Melakhim 5:7-8. In Sefer ha-mizvot Rambam cites three separate verses as sources for this prohibition: "You shall henceforth return no more this way" (Deuteronomy 17:16); "… by the way whereof I said unto you, 'You shall see it no more again' " (Deuteronomy 28:68); and "For whereas you have seen Egypt today, you shall see them again no more forever" (Exodus 14:13). In citing all three verses as negative commandments Rambam follows the Palestinian Talmud, Sukkah 5:1. The Babylonian Talmud, Sukkah 51b, however, cites only Deuteronomy 17:16. Maharsha explains that, for the Babylonian Talmud, Exodus 14:13 is a promise rather than a prohibition. Deuteronomy 28:68 is presumably viewed as a threatened punishment rather than as a prohibition. Basing himself upon the Palestinian Talmud, Rambam declares that the prohibition is limited to permanent residence. Accordingly, it is permissible to return to Egypt for business purposes or for other reasons which involve only temporary domicile. Rambam further rules that it is permissible to reside in Egypt if the land is conquered by "a king of Israel" with the approval of the Sanhedrin "since [the Torah] forbids [us] only return to [Egypt] as individuals or to dwell therein while it is in the hands of idolaters." The reason, as explained by Rambam, is that settlement in Egypt is forbidden because of the degenerate moral character of the ancient Egyptians. Reference to the immorality of ancient Egypt is made in Leviticus 18:13. Hence, when Egypt is under the dominion of Israel, Jews are permitted to reside in that land.

The nakedness of the sister of your mother you shall not reveal: To not have intercourse with the sister of the mother, as it is stated (Leviticus 18:13), "The nakedness of the sister of your mother you shall not reveal, etc." All of its content is like the sister of the father (Sefer HaChinukh 197).