Parashat Lech Lecha covers some of Abraham's most dynamic events, from leaving his home and family when he was 75 years old until the day he circumcised himself and all the males of his household when he was 99. Perhaps the most dramatic event in our parashah – indeed, arguably the founding event of the Jewish nation – is the Brit bein ha-Betarim, the Covenant between the Parts (Genesis 15:8-21).

The simple reading is that G-d forged the Covenant between the Parts with Abram after he rescued his nephew Lot in the battle of the four kings against the five (Genesis 14). However Seder Olam chapter 1 states that Abram was 70 years old at the time of the Covenant between the Parts, meaning that it happened while Abram was yet living in his father’s house in Haran.

The Targum Yonatan agrees with Seder Olam. The Torah tells us that “the dwelling of the Children of Israel that they resided in Egypt was four hundred and thirty years” (Exodus 12:40), which the Targum Yonatan renders, “the days that the Children of Israel dwelt in Egypt came to thirty Shmitta-years, which comes to 210 years; and there was a total of 430 years from when HaShem spoke to Abraham, from the time He spoke with him on the 15th of Nissan, [in the Covenant] between the Parts until the day they left Egypt”.

Accordingly, the Covenant between the Parts should be translated in the pluperfect. After Abraham’s defeat of the four kings (Genesis 14) G-d promised Abram that He would protect him, concluding with the words, “I am HaShem, Who brought you out of Ur of the Chaldees to give you this Land to inherit it” (Genesis 15:7)

Then the next verse is in the pluperfect: “He [Abram] had said: My Lord HaShem, how will I know that I will inherit [the Land]? And He had said to him: Take for Me three heifers…”, which introduces the Covenant between the Parts.

Forging His covenant with Abram, G-d told him: “Know with certainty that your descendants will be strangers in a land not theirs, and they will serve them, and they will oppress them for four hundred years…and the fourth generation will return here, because the iniquity of the Amorite will not be full until then” (Genesis 15:13-16).

In the event, though, as all the Talmudic and Midrashic sources are unanimous, we were in Egypt for 210 years, not 400 years. The 400-year countdown began not with the descent to Egypt, but with the birth of Isaac. Though G-d had long since promised the Land of Israel to Abraham and his descendants, they did not yet possess it (which was why when Sarah died, Abraham had to buy her burial plot from Ephron the Hittite) – so Isaac, Abraham’s first-ever “descendant”, was already “a stranger in a land not his”.

The history and chronology are clear enough. Levi, who went down to Egypt (Genesis 46:8-11, Exodus 1:1-2), was the great-grandfather of Moshe (Exodus 6:16-20) and of Korah (Numbers 16:1), both of whom left there at the end of the exile. Similarly, Hezron, who went down to Egypt (Genesis 46:12) was the great-grandfather of Nahshon (Ruth 4:19-20, 1 Chronicles 2:9-10), who was one of the tribal chieftains who left there (Numbers 7:12). Thus the third generation left Egypt, and after the forty-year delay in the Sinai Desert, the fourth generation after the twelve brothers and their sons returned to Israel.

Rashi explains the phrase “the fourth generation will return here” to mean “after they will be exiled to Egypt, they will be there for three generations, and the fourth will return to this Land” (and see also Rashi’s commentary to Exodus 12:40). And their return will be delayed “because the iniquity of the Amorite will not be full until then”, because, as Rashi explains, the Amorite will not deserve “to be cast out of his land until that time, because G-d never punishes a nation until its measure is full”.

That is to say, until the fourth generation of Jewish exiles, the Amorites were not yet sufficiently sinful for their expulsion from their land to be justified.

Nevertheless, Abraham’s descendants were redeemed from Egypt 430 years after the Covenant between the Parts, which was 400 years after the birth of Isaac. And they then wandered through the desert for the next forty years, until such time as the iniquity of the Amorite was full.

But a question still remains. If the fourth generation was to be redeemed, and if the 400-year countdown to redemption began with Isaac, then how could there be a 40-year delay between the Exodus and the return to the Land of Israel? Whatever the reason for the delay – that the iniquity of the Amorite was not full until then, and the sin of the spies (Numbers 13:1-14:34) – did that delay not contradict the pre-ordained schedule of redemption?

I suggest the following answer, which I base on Ketuvot 7b-8a and Rashi there:

When G-d created Adam, the first man, “male and female He created them” (Genesis 1:27). This means that G-d created Adam as a hermaphrodite – male and female in a single body (Eiruvin 18a, Ketuvot 8a, Bereishit Rabbah 8:1 et. al.). Later, He decided that “it is not good for Adam [man] to be alone” (Genesis 2:18), so He removed one side (often mistranslated as “one rib”) from him (verse 21), to form Eve, the woman, his wife.

This means that after the split, Adam and Eve were each only half a person, and only together were they complete. And the corollary is that when a baby is born, whether a boy or a girl, he or she is only half a person. The person – and in our context specifically the Jew – becomes complete when he and she stand together under the Chuppah and get married, when the male half and the female half are rejoined, “and they become one flesh” (Genesis 2:24).

This explains why there is no blessing over a new-born baby. After all – what can be more precious than a new-born Jew? How come we make no blessing over a Jew who has just come into the world? – Simply because we do not make a blessing over something that is incomplete. But when the Jew and the Jewess stand under the Chuppah and become one flesh, then indeed we say the blessing, “Blessed are You, HaShem, Who creates man [Adam]” (Ketuvot 8a, Kalla Rabbati 1:1).

So when Isaac was born, thirty years after the Covenant between the Parts, he was only half a person. For sure the countdown to redemption began that day; but just as Isaac was an incomplete person when he was born, the redemption 400 years later – the Exodus from Egypt – was likewise incomplete.

He became a complete person the day that he married Rebecca, “and Isaac was forty years old when he took Rebecca…as his wife” (Genesis 25:20). Hence the 400-year countdown to the day that Abraham’s offspring would return to the Land of Israel – the completion of the redemption – began forty years after the 400-year countdown to the Exodus.

The Covenant between the Parts was the beginning of the Jewish nation – but only the beginning. Parashat Lech Lecha closes with the 99-year-old Abraham circumcising himself and all the males of his household, thereby sealing G-d’s covenant in his flesh.

He was thereby elevated to the level on which his wife could conceive and bear his son Isaac (which will be one of the major themes of next week’s parashah), with whom the countdown to redemption began.