There is a rabbinic obligation at the Pesach seder to drink four cups of wine. The Talmud Yerushalmi gives a few reasons for the choice of four cups. They parallel the four redemptions that Hashem promised the Jews in Egypt (Shemot 6); they parallel the four references to Pharaoh’s goblet (Bereshit 40); they parallel the four kingdoms that have had or will have dominion over the Jews in exile; or, they parallel the four “cups of retribution” that the Jews’ oppressors will drink at the end of days.

In our texts of the Talmud (Pesachim 118a) there is no mention of an additional cup of wine. However, the text of the Rif mentions a fifth cup. The Rambam’s (8,10) view is more complex. He writes: “after, one washes and recites Birkat ha-Mazon on the third cup and drinks it; after, he pours the fourth cup and completes Hallel on it, and recites Birkat ha-Shir (yehalelukha Hashem kol ma’asekha), recites the blessing on wine, and tastes nothing more that night except water. He may pour a fifth cup and recite Hallel ha-Gadol (hodu la-Hashem ki tov until al naharot bavel), but this cup is not obligatory like the first four.”

What does the Rambam mean that the fifth cup is not obligatory like the first four? The Ran suggests two possibilities: that it is optional, or that it is for those who want to do the mitsvah in a better way. Interestingly, the Mehabber in the Shulhan Arukh does not mention a fifth cup, while the Rama quotes a view that if one is thirsty one may drink a fifth cup as long as one recites Hallel ha-Gadol before drinking it. Essentially this opinion considers it permissible, with the recital needed as a condition for permission. (I do not have an explanation for why the Mehabber rules like the Rosh, who rejects a fifth cup, against the views of both the Rif and Rambam; this contradicts his introduction, where he says that he rules according to the majority of the three authorities.)

On the surface the sources quoted by the Yerushalmi do not allow for drinking an additional cup of wine. The recital of Hallel ha-Gadol, which mentions the miracles of yetsiat Mitsrayim within a broader framework of Hashem’s miracles starting with creation, needs to be understood as well.

The dispute about Birkat ha-Shir, with one view that it is (or includes) Nishmat, may be the key. Nishmat reflects a broadening of praise to Hashem for all the miracles of life. At this point in the Seder we move beyond focusing on yetsiat Mitsrayim to praising Hashem for all the miracles done for the Jewish people throughout history. The fifth cup places yetsiat Mitsrayim in a larger context. This is not obligatory, as the night’s primary mitsvah issippur yetsiat Mitsrayim, but it may be an enhanced mitsvah according to one understanding of the Rambam.

The Rabad connects this fifth cup with ve-Heveti, an apparent fifth term of redemption that somehow was not mentioned by the Yerushalmi.

There are three explanations why ve-Heveti is not counted as a fifth term of redemption. The Ramban in his introduction to Shemot writes that the redemption was completed by the building of the Mishkan and was not dependent on coming to Israel. Since ve-Heveti refers to Hashem’s bringing us to Israel, it is a post-redemption term, not a term of redemption itself. Second, the generation that left Egypt did not merit entering the land. Alternately what is different is that the four terms of redemption refer to actions by Hashem for the Jewish people, without their need to participate; coming to Israel, however, required an active role by the Jews.

All three fit into the idea that the mitsvah of sippur yetsiat mitsrayim ends with the drinking of four cups but the full relationship of the Jews and Hashem and the total redemption incorporates a voluntary fifth cup.