Wine is considered a royal drink, one that symbolizes freedom. It is the appropriate beverage for the nights when we celebrate our freedom from Egyptian bondage.
Many reasons are given for drinking four cups of wine. Here are some of them:
When promising to deliver the Jews from Egyptian slavery, G‑d used four terms to describe the redemption (Exodus 6:6-8): a) "I shall take you out..." b) "I shall rescue you..." c) "I shall redeem you..." d) "I shall bring you..."
The four cups symbolize our freedom from our four exilesWe were liberated from Pharaoh's four evil decrees: a) Slavery. b) The ordered murder of all male progeny by the Hebrew midwives. c) The drowning of all Hebrew boys in the Nile by Egyptian thugs. d) The decree ordering the Israelites to collect their own straw for use in their brick production.
The four cups symbolize our freedom from our four exiles: The Egyptian, Babylonian, and Greek exiles, and our current exile which we hope to be rid of very soon with the coming of Moshiach.
The words "cup of wine" are mentioned four times in Pharaoh's butler's dream (Genesis 40:11-13). According to the Midrash, these cups of wine alluded to the Israelites' liberation.
According to Kabbalah, there are four forces of impurity (anti-divinity, or kelipah). On Passover, when we celebrate our physical freedom, we also celebrate our liberation from these spiritual forces. Our physical departure from Egypt was a reflection of our spiritual one—we were pulled from the clutches of depravity and impurity and set on the path to receiving the Torah and connecting with G‑d.