The Bais Halevi (end of Drush 2) brings a Medrash on a posuk in Eichah השביעני במרורים “Hisbi’ani bamerorim, hirvani la’ana.” The Medrash says that this posuk is a remez that the first day of Pesach and Tisha Ba’av fall on the same day of the week, a rule which we know as “Aht Bash” etc. So we see that in Megillas Eichah, which is the description of Tisha Ba’av, there is a passuk that refers to Pesach, and also that the day of the week that the seder falls on is connected to Tisha Ba’av. The Bais Halevi asks, why on Earth would there be such a connection? What does Pesach, the celebration of the redemption from Mitzrayim, have to do with Tisha Ba’av, the day we mourn destruction and exile?
He then asks another question. If ‘merorim’ is a reference to moror, why would it be predicated by the word Hisbi’ani (‘he satiated me’)? We certainly don’t need to eat maror to satiation. (In fact, mid’orayso, you are yotzei maror with a tiny little piece, and you only need a kezayis because the brocho states “ahl achilas maror”, as the Rosh says in Pesochim.) The answer is, though, that according to Hillel we eat the moror together with the meat of the korbon peisach, and since the korbon is eaten when we are full– al hasova– the taste of moror remains in our mouth when we are satiated. But why would the Torah require that the taste of bitterness remain in our mouth after we ate the korbon pesach? After all, we eat moror because there was commemorate slavery and redemption on the same night, but it ended with redemption. So why leave the taam moror for the end and remain with that taste in our mouths?
The answer to both questions is this: we were supposed to be in Mitzrayim 400 years. But “Hakodosh boruch hu chisheiv es hakeitz,” which means that since we were almost assimilated into Mitzrayim, we were on the 49th level o f Tumah, we had to leave then or we would have lost our identity forever. But our early exit from Mitzrayim came with the price of a future golus to make up for the early end of that one. Therefore, we are meramez that the seed of Tisha Ba’av was planted at the moment of the geula from Mitzrayim, which is commemorated by the Korbon Pesach. It was a great redemption, but not a perfect redemption.
And see above Shemos 5:3, that Moshe asked Pharaoh to let them out to be serve Hashem for three days, to be makriv korbonos. Why the duplicity? Why not just confront Pharaoh with the demand to leave? With this we can see that his cheshbon might have been that if they were makriv, maybe the chizuk would have reinvigorated their faith and identity, it would have brought them back from the 49th level of tumah, and thus they would be able to stay the whole 400 years, so that the geula would have been a perfect and permanent one without a Tisha Ba’av to follow. The way Harav Reuven Feinstein shlita said it was that sometimes achishenu can be later than b’ito, which he explained with a reference to the mistake that Belshatzar and Korosh and Achashveirosh made in interpreting the ‘70 years’ of golus. What he means is that an achishenu might leave an outstanding balance which will have to be paid later, so it really extends the problem. Therefore, B’ito is faster than Achishenu.
I also saw that the Malbim says exactly the Beis Halevi’s vort, including the Medrash, in Eicha 3:15. (By the way, the Beis Halevi was long before the Malbim.)
When I said this in shul, someone remarked that we’ve paid over ten times as much as the outstanding number of years! I answered, and this is important to incorporate into the vort, that what it means is that the birth of Klal Yisroel was in a state of potential avdus, that there was a chiyuv of avdus/golus hanging over us. This admixture of avdus into our identity expresses itself in our being subject to golus. In other words, it’s not payment for the years we owe, it’s an element of our identity and our fate. Or, (and probably better for preventing complaints, but possibly not exactly what the Beis Haleivi means,) the geula from Mitzrayim was imperfect. It was glorious, it was with nissim and niflo’os and the Yad Hashem, but it was imperfect, because while it did take us out of Mitzrayim, there remained a shemetz of avdus on and in us. (♫You can take the Jews out of Mitzrayim but....)