At the conclusion of רמב"ם’s description of what we do at the סדר, he writes that it is permissible to mix a fifth cup of wine, and recite upon it לדוֹג ָלָה ָל ָה ָ (this is קלוָפרק in תהלים, in which there are 26 פסוקים, each concluding with the words כ ָיָל ָעוֹל ָםָח ָס ָדוֹ). This cup is not an obligation like the other cups.
Question
If the רמב"ם holds that one needs to drink a fifth cup of wine, why does he say that it is not an obligation? And if he holds that it is not an obligation, why does he write that it is not an obligation like the other cups (which seems to imply that there is some degree of ח ָיוּב)?
Answer
When the רמב"ם describes each of the earlier 4 cups, he clearly mentions drinking each one. However, when he discusses the 5th cup, he does not say anything about drinking it. We can understand that the רמב"ם is suggesting that we fill a 5th cup, say הללָהגדול over it, but not actually drink it. Because although the הלכה is – as we do today – that we only drink 4 cups of wine at the סדר, there is actually an opinion in the גמרא that says we should drink a 5th cup as well. To satisfy both opinions, רמב"ם suggests that we fill a 5th cup with wine, but that we do not actually drink it.
Further discussion
Where else in הלכה do we see an example of filling a cup of wine that we will not drink? (See אותָג in the שיחה)
In those days, the wine was strong, and had to be mixed with water before drinking.
