The Halachah requires only that we consume the better portion of our wine glass during the Seder. We lean to the left when we drink each of the four cups, but there is no imperative to drain the cup. Assuming the cup contains the minimal amount required, a little over 3 ounces, we need to drink just over half of it, less than two ounces of wine. This is true for all four of the cups. Nevertheless, common practice is to drain the fourth cup, drinking all of it. The reason is obvious, and it is similar to the practice of drinking the entire cup of wine when reciting Havdalah. While the first three cups are going to be followed by more drinking, and therefore no after-blessing will be recited regardless of the quantity consumed, the fourth glass marks the end of drinking. If a proper quantity of wine (revi’it, or just over 3 ounces) was consumed, such an after-blessing is warranted. If one has consumed less than that, leaving wine in the glass, no blessing follows. It is therefore customary to drain the fourth glass, generating a requirement for an after-blessing, similar to Havdalah, after which no further drinking normally follows.
This is the standard reason given for this practice. There is no imperative to drain the fourth glass, it is only desirable in order to generate an after-blessing. Some commentaries, however, attribute more significance to draining the fourth glass. Rabbi Chaim Ingram, of Sydney, Australia, penned an article this year, suggesting a delightful idea to explain the significance of draining the fourth glass. We know that the sages instituted the four cups during the Seder to correspond to the four terms of redemption used by the Torah when Hashem promised to redeem Israel:
Vehotzeti (I will bring you out) – the first term – signifies the removal of the burden of slavery. This occurred once the plagues began. Most commentaries understand that the slavery was discontinued once the plagues started.
Vehitzalti (I will save you) – the second term – reflects the removal of any subordination to the Egyptians. This occurred before the final plague, when each family of Israel took a lamb and tied it to the bed-post in defiance of the Egyptian deity.
Vega’alti (I shall redeem you) – the third term – alludes to the physical removal of the people from Egypt. This took place when they marched across the desert and through the Red Sea.
Velakachti (I will take you) – the fourth term – expresses the bond established at Mt. Sinai, when a covenant established an unbreakable relationship between God and Israel.
When we drink the first glass, corresponding to the end of slavery, the cup need not be drained. We can live as Jews even in a state of slavery, as our ancestors did in Egypt. They succeeded in preserving their identity and character. The Midrash notes that throughout the generations of their stay in Egypt the Israelites did not change their names, their language of their dress. This includes the 80 years of actual slavery. Thus, it is possible to remain true to our mission and to God despite such hardships. Drinking the majority of the first cup is thus adequate, although it is not drained completely. The Vehotzeti stage can be partial.
The second cup represents the next stage of removal, the release from subordination to Egyptian rule. Since leaving Egypt the vast majority of our national experience has been under the rule of a foreign nation and government. Despite this we have succeeded in preserving our character, even developing the great body of Talmudic literature that forms the backbone of Jewish lore and tradition. Indeed freedom from subservience is not a condition of living as a full Jew. This second cup can also be left with some wine; a partial redemption from subservience can also be adequate.
The third cup, Vega’alti, represents our physical removal from the state of exile. This was another stage in our redemption from Egypt, and this too is a condition we can live, and have lived, without. During many centuries of the long exile Jews were repressed and oppressed by their host nations. But today in most first world countries where Jews reside they are free to practice as Jews without significant constraints. There is no slavery, not even subordination, but we remain in our Diasporic homes. Vega’alti can also be partially fulfilled without restricting our ability to be fully Jewish in character. The third cup need not be drained in its entirety.
Different from the first three, however, is the fourth cup, signifying the covenantal bond established with the Almighty at Mt. Sinai through the revelation and the giving of the Torah. This is something the Jewish people cannot live without. A full draining of this cup Velakachti is necessary, as it cannot be partially fulfilled. This is a stage, a condition of redemption, where we cannot compromise or suffice with a mere portion. We drain this cup entirely.