Classics and Beyond Pesach: great reason we have 4 cups by Seder

A clever pshat in an interesting gemora and a great reason why we have 4 cups by Seder

ומושב בני ישראל אשר ישבו במצרים שלשים שנה וארבע מאות שנה
Now the sojourning of the people of Israel, who dwelt in Egypt, was 430 years (Shemos 12:40).

The Gemara (Sanhedrin 91a) describes a legal claim the Egyptians brought before Alexander the Great. They were trying to recoup the vast fortune that the Yidden had taken from Mitzrayim at Moshe’s behest. Their argument was that the Jews had only borrowed this great wealth, and now it needed to be returned.
Geviha ben Pesisa advocated on behalf of the Jews. His counterclaim was that 600,000 people left Egypt (Shemos 12:37), who had been in Egypt for 430 years (ibid. V.40).1 Geviha demanded, “Pay us wages for that many people working for those many years.” After thinking it over for three days, the Egyptians realized that whatever was taken from their country was not adequate compensation for all those years of servitude.
Case dismissed!
Yet, the Maharsha asks an obvious question: We did not work in Mitzrayim for 430 years. We weren’t even there that long; we were only in the country for 210 years. And most of those years were not spent as slaves. When we first descended to Egypt, we were treated royally. We were the family of Yosef, the savior of Egypt. Only after all the shevatim died did the mistreatment begin.
In fact, the Midrash (Shir HaShirim Rabbah 2:11) writes that there were only 86 years of hard work. (The gematria of אלה-ים, which alludes to Middas HaDin, is 86.) These years began from the birth of Miriam, Moshe’s older sister; that is why she was called Miriam, which comes from the root of מר, bitter, since that was when the Egyptians began to embitter the lives of the Jews, as it is written, “Vayemareru es chayeihem ba’avodah kashah – They embittered their lives with hard work” (Shemos 1:14).
So how could Geviha ben Pesisa state that we were there for 430 years and claim wages for all those years? The Maharsha says that the 86 years were so harsh that it was like 430 years.
Rav Marcus Lehmann, in his Haggadah shel Pesach, explains it differently. It’s true that we did not work for 430 years, but only 86. On the other hand, although 600,000 people left Egypt, five times that amount did the actual work. The Torah tells us, “Va’chamushim alu Vnei Yisrael mei’eretz Mitzrayim – And the Children of Israel were armed when they went up from Egypt” (Shemos 13:18). Rashi gives an alternative definition for the word chamushim, armed. חמשים can come from the word חמשה, which means five; one fifth of the Bnei Yisrael ascended from Egypt, while four fifths died during the Plague of Darkness.
Thus, three million people worked for 86 years, which is the same as 600,000 people working for 430 years: 600,000 x 5 =3,000,000; and 86 x 5 = 430.
Geviha ben Pesisa did not have to fear that the Egyptians would question the validity of his claim, even though he said that the Jews had been in Egypt for 430 years. For if they would have countered that this was not the case, he could have brought up the abovementioned fact.
Rav Lehmann writes that based on this, we can bring a hint to why we have four cups at the Seder. כוס, cup, is 86 in gematria. We raise the כוס four times to thank Hashem for the four times כוס – 4×86 – which he took off of the calculation. By all rights, we should have worked for 430 years, five periods of 86, or כוס. (Our accounting of 430 years actually began from the bris bein habesarim, when Avram was told that his children would go into exile. The 400 years that Hashem told him about at that time began with the birth of Yitzchak; see Rashi Bereishis 15:13.)
Hashem, in His kindness, only had us work for 86 years, one period of כוס.
This is as it says in Tehillim (116:13): “Kos yeshuos essa u’ve’Sheim Hashem ekra – I will raise the cup of salvations and the Name of Hashem I will invoke.”