שמות פרק ו, ו לָכֵן אֱמֹר לִבְנֵי-יִשְרָאֵל אֲנִי ה' ו הוֹצ אתִי אֶׁתְכֶׁם מִתַ חַת סִבְלֹת מִצְרַיִם ו הִצ ל תִיַ אֶׁתְכֶׁם מֵעֲבֹדָתָם ו ג א ל תִי אֶׁתְכֶׁם בִזְרוֹעַ נְטוּיָה וּבִשְפָטִים גְדֹלִים ז ו ל ק ח תִיַ אֶׁתְכֶׁם
ירושלמי מסכת פסחים דף סח/ב פרק י הלכה א מניין לארבעה כוסות רבי יוחנן בשם ר' בנייה כנגד ארבע גאולות והוצאתי והצלתי וגאלתי ולקחתי
All the commentators discuss the four expressions (לשונות) of Geulah. However, the Yerushalmi does not use the word לשונות. According to Rabbi Epstein the Yerushalmi is intentional and accurate in using “redemptions.”
It is not sufficient to establish 4 cups of acknowledgement for the four expressions of geulah. Rather, the 4 cups were establishment for the 4 periods of Geulah. Each of the words of Geulah in the verse represents different periods of redemption for the Jews in Egypt, with each period different and in order, each necessitating its own thanksgiving (different cup to be displayed at the Seder).
והוצאתי – that HaShem took the Jews out of the severe part of the servitude of the Egyptians, yet they remained enslaved without freedom.
והצלתי – that HaShem removed the Jews completely from servitude, but yet they lack redemption.
וגאלתי – that HaShem redeemed them, yet they lack purpose
ולקחתי – that HaShem took the people to become His nation
Now one can understand the different levels of redemption, each one greater than the previous one. Each level requires acknowledgement and thanksgiving, for which the Rabbis established the concept in deed through the four cups of acknowledgement.
And one might think to establish a fifth cup, for the word והבאתי. It is not because it is not a part of the redemption process. Rather, we all remain in Exile today, lacking the final Redemption, with our land partially (or at times) fully controlled by those not sympathetic to G-d. Therefore, we do not drink a cup of wine regarding the final Redemption. And perhaps the cup designated for Eliyahu alludes to this final step of redeeming all of us from the final Exile.
