How Long Were Bnei Yisrael Slaves in Egypt? by Rabbi Aaron Levitt

(13) And He said to Abram, “Know well that your offspring shall be strangers in a land not theirs, and they shall be enslaved and oppressed four hundred years;

(1) ושני חיי קהת … ושני חיי עמרם וגו׳ AND THE YEARS OF THE LIFE OF KOHATH WERE etc. … AND THE YEARS OF THE LIFE OF AMRAM WERE etc. — From these numbers we may gather regarding the period of residence of the children of Israel, — viz., four hundred years, of which Scripture speaks, that these four hundred years were not passed in Egypt alone, but that they date from the day of Isaac’s birth. You know that Kohath was one of those who went down to Egypt; now reckon all his years (133) although really we should not take into account the years he lived before he went down to Egypt, and the years of Amram, his son (137), and the eighty years of Moses, the latter’s son, which he had attained when the Israelites left Egypt, and you will not find them totaling to four hundred, and in this calculation many years of the sons’ ages are included in those of their fathers (i. e. in such a calculation one must deduct in each instance the father’s age when his son was born since this number is included in the total age of each of these persons) (cf. Rashi on Exodus 12:40)

(1) We are forced to say that Scripture left out some of the generations between Kehat and Amram, for in [Numbers 3:28] the count for Kehat of all the males from a month and up was 8,600, and he only had four sons as his family, so each of those four sons would [have had to] have 2,150 sons. And behold Amram only had Aaron, Moses, and Miriam. Moses only had two sons, and Aaron four, so how is is possible for Amram, Yitzhar, Chevron, and Uziel to have 2,150 souls [each] in the second year after leaving the land of Egypt? Therefore, one must conclude as IB Koppe in his essay, "Israelitas non 215, sed 430 annos in Eagypt commoratos esse," Gottinga 1777, where he said (and Rossenmueller agreed with him) that Levi, Kehat, and Amram were not in sequential generations, but rather other generations were between them. And according to this, one can answer as its plain meaning the number of 430 years that Israel was in Egypt [Exodus 12:40]. And according to this, the powerful procreation of the Israelites in Egypt can be understood, which the Torah did not speak of as an actual miracle. And the wise Jost (Volume 1 page 2) said that the names mentioned here are family names, so it is saying that so long as the father was still alive, the children stayed bonded together as one family for the most part (even though sometimes sons would divide their fathers household, as was the case for Isaac and Ishmael in the lifetime of Abraham, and Jacob and Esau in the lifetime of Isaac), and with the death of the father the family would split, and sometimes even after the death of the father they would not split off until some time. So the plain meaning of this section according to his opinion is that the family of Levi remained one family unit, and was called "Levi" for the span of 137 years after the death of Jacob, and then, after Levi died, the family split into three, the names of which being Gershom, Kehat, and Merari. So, the family of Kehat stayed as one unit for 133 years, and afterward it was split into four families. And at the time of the exodus from Egypt, 137 years had already passed, and the Amram family was one family, of which came Moses and Aaron. So if you add together the three numbers of 137, 133, and 137, and add 17 years on that for how long the Israelites were in Egypt before Jacobs death, you have 424 years, meaning close to 430 years. Therefore (he says) whenever it says "the son of Yitzhar", "the son of Kehat", etc, it means "the descendant of Yitzhar", "the descendant of Kehat".

The Gemara continues: And this was due to the incident of King Ptolemy, as it is taught in a baraita: There was an incident involving King Ptolemy of Egypt, who assembled seventy-two Elders from the Sages of Israel, and put them into seventy-two separate rooms, and did not reveal to them for what purpose he assembled them, so that they would not coordinate their responses. He entered and approached each and every one, and said to each of them: Write for me a translation of the Torah of Moses your teacher. The Holy One, Blessed be He, placed wisdom in the heart of each and every one, and they all agreed to one common understanding. Not only did they all translate the text correctly, they all introduced the same changes into the translated text. And they wrote for him: God created in the beginning [bereshit], reversing the order of the words in the first phrase in the Torah that could be misinterpreted as: “Bereshit created God” (Genesis 1:1)...

Instead of: “And the residence of the children of Israel, who resided in Egypt, was four hundred and thirty years” (Exodus 12:40), which when read literally is imprecise, for they did not dwell in Egypt that long, they wrote: And the residence of the children of Israel, who resided in Egypt and in other lands, was four hundred years.

Blessed is the One who keeps his promise to Israel, blessed be He; since the Holy One, blessed be He, calculated the end [of the exile,] to do as He said to Avraham, our father, in the Covenant between the Pieces, as it is stated (Genesis 15:13-14), "And He said to Avram, 'you should surely know that your seed will be a stranger in a land that is not theirs, and they will enslave them and afflict them four hundred years. And also that nation for which they shall toil will I judge, and afterwards they will will go out with much property.'"