Question: Is it permissible to substitute grape juice for the
four cups of wine at the Seder?
Answer: The four cups (or five, according to the custom that I
follow) of wine consumed at the Seder are a special manifestation and
fulfillment of our sense of freedom: we feel altogether free after drinking
four cups of wine! Since there is no comparable feeling that results from
drinking grape juice, Rav Moshe Feinstein z"l rules that one should
ideally drink wine. However, if it is difficult for a person to drink wine,
it is permissible for him/her to use grape juice instead.