"You Shall Tell Your Child On That Day, Saying,
'It is because of what the LORD did for me when I came out of Egypt.'
'' (Exodus 13:8)

The meals in celebration and remembrance of deliverance
from bondage.
Said by some of the most elitist of Rabbinim, there really now should be 5 cups of wine, since we (In Israel) have entered the land, but it is
hard to break from the tradition. Good Wine is considered the choicest drink for the occasion, without one become drunk, if need be, to add
grape juice or other. The celebrations is that which symbolizes freedom. It is the appropriate  drink for the nights that are in celebration of
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..."