Musar su Genesi 15:13

Here is an instance that shows that the sequence in which the Torah reports events is not necessarily the chronological order in which things occurred. Remember that Abraham was seventy years old at the time of the covenant between the pieces in 15,18 (as we know on the authority of סדר עולם). Our sages also consider the count of the four hundred years that the Torah mentions in that covenant (15,13) as commencing with the birth of Isaac. When Exodus 12,40 mentions a period of 430 years that the Israelites "resided" in Egypt, our sages compute that period as having commenced at the ברית בין הבתרים "the covenant between the pieces," i.e. when G–d revealed Himself to Abraham in 15,1. [Rashi's commentary that this number includes the years spent elsewhere as strangers by Abraham and his descendants, may be based on the letter ו (and), before the word מושב in 12,40. Ed.]

(Ibid. 14): "And he [Jacob] sent him [Joseph] from Emek Chevron" — "from the deep [(alluded to by "Emek")] counsel of that tzaddik [Abraham] buried in Chevron, in fulfillment of what was stated (Ibid. 15:13): 'for your seed will be a stranger in a land that is not theirs.'" The meaning here (in my humble opinion) is that Egypt was the "nakedness of the land," an extremely impure place, for which reason it was ordained in the beginning that one of the sons of Jacob would come to publicize there [in Egypt] belief in the Divine providence, as it is written (Ibid. 41:25): "What G-d is to do He has shown to Pharaoh." For a similar reason Joseph commanded afterwards that they [the Egyptians] circumcise themselves — all to weaken the power of impurity, so that it would be fit afterwards for Israel to sojourn there.

We can better understand the reason that the Torah permits Edomites and Egyptians (of the third generation after conversion) to become fully fledged members of the Jewish people if we take a look at the historical development of Abraham, the first convert to Judaism. Both the second generation after Abraham, i.e. Isaac-Ishmael, and the third generation, i.e. Jacob-Esau, still contained a considerable amount of פסולת, spiritual refuse. Only the fourth generation of Abraham's descendants, Jacob's sons, were completely pure and had divested themselves of their spiritual waste. Esau actually became the means that Jacob received the blessing. As a recognition of this the third generation of converts descended from Esau/Edom are admitted as full fledged members. The Torah acknowledges this in 23,8: "Do not despise Edom for he is your brother;" this means that after living as a Jew for the third generation Esau once more qualifies as a brother of Jacob not only biologically but also spiritually. The same law applies to the absorption of Egyptians into the community of the Jewish nation. Our exile in Egypt actually commenced at the time G–d foretold Abraham about it at the covenant of the pieces in Genesis 15,13. Abraham was told that the fourth generation of his descendants would return to the land of Canaan. While in Egypt, the souls of the Jewish people were refined to the extent that they were able to become a nation comprising over 600,000 men of military age, a people that qualified for the title "Israel," the honorific title bestowed by G–d on Jacob. It is appropriate therefore that the third generation of an Egyptian convert to Judaism should enjoy full equality with other Jews just as Jacob who was the third generation counting from Abraham's conversion, was pure and had shed all the spiritual פסולת which had remained from the pollutant of the serpent. Israel, too, had remained גרים, strangers, in Egypt for three generations. The prohibition of bringing the wages of harlotry to the altar of G–d is explained simply by the fact that the harlot is beholden to Lilith, the antithesis of the שכינה. It is a domain where the dogs cry out because the angel of death is constantly around. This is why David prayed in his Psalm 22,21: "Save my life from the sword, my precious life from the clutches of a dog."