Explanations for Four Cups of Wine at Passover Seder

At the Passover seder, Jews usually drink four cups of wine while leaning to the left, according to the Haggadah service, but the reason why is elusive to many. Considered a royal drink, wine symbolizes freedom, which is what the Passover seder and Haggadah celebrate. 

Possible Explanations

In Genesis 40:11-13, when Joseph interprets the dream of the butler, the butler mentions the word "cup" four times. The Midrash suggests that these cups alluded to the liberation of the Israelites from Pharaoh's rule.

Then there is God's promise to take the Israelites out of Egyptian slavery in Exodus 6:6-8, in which there were four terms used to describe the redemption:

1. I shall take you out ...
2. I shall rescue you ...
3. I shall redeem you ... 
4. I shall bring you ... 

There are four evil decrees by Pharaoh that the Israelites were liberated from, including:

1. Slavery
2. The murder of all newborn males
3. The drowning of all Israelite boys in the Nile 
4. The order for the Israelites to collect their own straw to make bricks

Another opinion cites the four exiles that the Israelites suffered and the freedom that was (or will be) granted from each, including:

1. The Egyptian exile
2. The Babylonian exile
3. The Greek exile
4. The current exile and the coming of the Messiah

There's a reason provided, also, that in the Haggadah Jews read about the forefathers Abraham, Isaac, Jacob, and Esau, and Jacob's son Yosef, but the matriarchs do not appear in the narrative. This view suggests that because of this, each cup of wine represents one of the matriarchs: Sarah, Rebekah, Rachel, and Leah.

The Cup of Elijah is the fifth cup that appears at the seder.