Can Egypt's genealogy give exact years there?
The genealogy does not allow the years in Egypt to be calculated with certainty, because it may omit generations and was not necessarily intended as a complete chronological register. The period most generally supposed is about 215 years, while the 430 years are reckoned from the patriarchal sojourn and promise through the Exodus; even so, the duration remains an unsettled question. Kohath was born before Jacob went down, since he entered Egypt with Levi’s family. The exact time when Kohath fathered Amram is not stated, though the usual reconstruction places the later generations in Egypt; Jochebed, Moses’ mother, is explicitly said to have been born there.
Kohath went into Egypt with Levi’s family
Son of Levi, and his descendants. He was the grandfather of Moses and Aaron. Of Kohath little is revealed: he went into Egypt with the rest of his brethren and died at the age of 133 years.
The genealogy gives four generations, not ten
A much shorter period is implied in Gen. 15:16, which says of Israel in Egypt that "in the fourth generation they shall come hither again;" and if we turn to Ex. 6:16-20 we find exactly four generations, thus: Jacob's son Levi. Levi's son Kohath. Kohath's son Amram. Amram's son Moses.
The usual reckoning makes Egypt about 215 years
Levi lived only a hundred and thirty-seven years in all, and supposing (it can be approximately proved) that he lived in Egypt eighty-eight years, Jochebed was born during those years. If Moses was born when she was forty-seven years of age, and Moses was eighty years old at the Exodus, these sums (88 + 47 + 80 = 215 years) show that Israel may have been in Egypt about two hundred and fifteen years, and this is the period now generally supposed.
The 430 years include the patriarchs’ sojourn
It is better to take the four hundred and thirty years as including the sojourn of Abraham (after the promise), and of Isaac, and of Jacob, though strictly speaking Abraham, Isaac, and Jacob were not 'children of Israel.'
The length of Egypt’s sojourn remains unsettled
But the duration of the sojourn is a very obscure point; Josephus gives it both as two hundred and fifteen and as four hundred and thirty. The reader may see Fynes Clinton's investigation of the point, if he have access to it. He reckons two hundred and fifteen years, taking the shorter or Hebrew chronology. Many able chronologists doubt of this, as Hales. At first sight Galatians 3:17 seems to decide the question, but when examined it does not, I think, necessarily do so.
“Begat in Egypt” does not settle every generation
This verse (59) is the greatest difficulty of all as to the counting 430 years of captivity. I do not see that the 430 years of Galatians 3 is so much so, because it must, if strictly taken, refer to Israel's offering, for the covenant was kekuromenen (confirmed), i.e., some forty years after the arrival in Canaan; and the term here "begat to him in Egypt" implies, it would seem, it was one (i.e., Levi himself) who had come down, so that it might have been otherwise.
Genealogies may omit generations and family links
Yet we should quickly note that if one wants to enter into the details of the subject before us, one must be very guarded in his conclusions, for Jewish genealogies present innumerable difficulties. First, very frequently those who are called the son of so-and-so are not necessarily his children at all, but his grandsons, or even his grandnephews. Then there are cases where the head of a clan is regarded as the father of a generation, all the generations between being omitted. There are cases where through the "right of redemption" a distant relative (see the Book of Ruth) becomes the head of an extinct family. There are those cases, very frequent during the captivity, where one family took a place in the inheritance of another family which had disappeared, without being related by direct descent to the head of that race. There are cases too where, the name of ancestors being missing, the name of the birthplace replaced, so to say, the name of the family head. There are cases, common among the Jews, where a person had more than one name (see, for example, these well-known names: Benjamin and Benoni, Reuel and Jethro, Solomon and Jedidiah, etc.). And lastly there are cases where an abridged genealogy was given, the names indicated being nothing more than a few pointers to establish the line of descent.