In Parshat Vaera (Shmot 6:6-8) God tells Moshe "Say to B.nai Yisrael I am God Vehotzeiti- I will bring you out from under the burdens of Egypt, Vehitzalti- I will save you from their slavery. Vega.alti- I will redeem you with an outstretched arm and with acts of great judgments. Velakachti- I will take you to Myself as a people and I will be your God. You will know that I am your God who is bringing you out from under the burdens of Egypt. Veheveti- I will bring you to the land regarding which I raised my hand in oath that I would give it to Avraham, Yitzchak and Yaakov, and I will give it to you as an inheritance. I am your God."

In these three psukim we see five words of redemption- vehotzeiti, vehitzalti, vega.alti, velakachti and veheveti.

In the Gemara (Yerushalmi Psachim) Rabbi Yochanan asks: "Why do we drink four cups of wine on Pesach?" The four cups of wine correspond to the four words of redemption vehotzeiti, vehitzalti, vega.alti, velakachti.

Why don.t we drink a fifth cup to correspond to the word veheveti?

According to Torah Temima, this last promise has not fully been fulfilled. Even though B.nai Yisrael were brought to the land of Israel, they were subsequently exiled and many of the Jewish people still remain in Galut (exile).

Another idea is that the exodus from Egypt was certain- God took care of everything while the settling and building up of Israel is up to us and has not yet been completed.

At the Pesach seder, we pour a fifth cup of wine, the cup of Eliyahu, which we don.t drink, to symbolize the fact that we hope that the full promise of redemption will be fulfilled and that all of the Jews will return to Israel. We pray that speedily Eliyahu will come and at that time the full redemption will take place.