Why do we celebrate holidays that commemorate things that happened in the past? Rabbi Nathan Lopes Cardozo addresses this issue in his book Crisis, Covenant and Creativity:

Since our Tradition derives from events that took place in the past, there is a strong urge to place the emphasis in Judaism on the past.  And yet, to do so would be to misconstrue the very essence of our religion. However significant the past may be, its value lies primarily in its ability to inform the future.  To stay genuine, the epic Jewish experience must be re-lived, now and in the future, giving birth to exciting elements that continue to create wonder and anticipation.

Observant Jews, therefore, never memorialize their great history.  Rather, they celebrate the events of their people’s distant past as if they took place in the present day.  During Pesach, the Jew sits at the Seder table and tells the story of the exodus from Egypt in such a way that he re-experiences it.  He is obligated to create and atmosphere in which he and his family feel as though they themselves were slaves in Egypt, and who are now able to enjoy freedom.  The famous Chassidic saying that Pesach is not so much about how the Jews got out of Egypt, but how Egypt and its mentality gets out of the Jews, beautifully illustrates this point.  Halachically, Pesach has to be experienced in a way that transcends history, and thereby illuminates the present. (Crisis, Covenant and Creativity, pgs. 140-141)

What are you going to do to accomplish this at your seder?