Sefer HaChinuch ספר החינוך

To not ever dwell in the Land of Egypt: That we not further go back on the way to Egypt ever; meaning to say that we do not establish our residence in Egypt. And about this is it stated (Deuteronomy 17:16), “and the Lord said to you, ‘You shall not further go back on this way again.’” And the prevention of this is repeated three times: They, may their memory be blessed, said (Mekhilta DeRabbi Yishmael 14:13:2), “In three places did the Torah warn not to return to the Land of Egypt [...] In the three they returned, and in the three they were punished.” And these three places [are] the one we mentioned; the second is “by the way that I said to you, ‘You shall not further again, etc.’” (Deuteronomy 28:68); and the third is “as that which you see Egypt today, you shall not further, etc.” (Exodus 14:13) — and even though it appears to be [only] a story from its revealed meaning, the tradition comes about it that it is a prevention (a negative commandment).

It is from the roots of the commandment that [it is] because the people of Egypt are bad and sinners. And God, blessed be He, took us out from there and redeemed us, in His kindnesses, from their hand to give us merit, to walk in the ways of truth. And in His great goodness upon us, He wanted that we not return again to become defiled among them, so that we not learn from their agenda and that we not walk in their disgusting ways, in view of our perfect Torah.

From the laws of the commandment is that which they, may their memory be blessed, said (Sukkah 51b), that it is not just the city of Egypt which is included in the prohibition, but rather it is forbidden to dwell in all of Alexandria. And from the Sea of Alexandria for the length of four hundred parasangs and for the width of four hundred parasangs is [all included] in this prohibition. And the rest of its details are clear.

And this prohibition is practiced in every place and at all times by males and females. And one who transgresses it and establishes his residence there violates this negative commandment. But we do not administer lashes for this negative commandment, since no act is [involved] with it. As at the time of the entry, it is permitted, and there is no act in his lingering there. And Rambam, may his memory be blessed, said (Mishneh Torah, Laws of Kings and Wars 5:8) that if a king of Israel conquers the Land of Egypt according to the word of the court, it would be permissible for us to dwell in it. And “the words of the wise are grace.”