“You must not act in the manner of the people of the land of Egypt”
Rashi comments that, of all nations, Egypt had the worst moral decay. The Jewish people that dwelt in their midst were drawn to their decadent way of life. Thus, the Exodus is to be seen not only as a physical redemption but as a spiritual one as well. Had Israel remained a minute longer, the nation would have been spiritually lost.
Hence the seder’s focus on the principle: “In every generation a man must regard himself as if he himself came forth out of Egypt” (Talmud Pesachim 116:b). Reciting the Passover story, as we do in the haggadah, is a mitzvah — so why is it there no blessing before doing it? Some argue that there is indeed a blessing — included within the berachah of asher gealanu recited just before the meal, when one has in essence finished telling the story of redemption. But this explanation is unclear.
Blessings are normally recited before a mitzvah. The great Chatam Sofer explains this difficulty: we couldn’t make the blessing before we began the story because, according to the Talmudic statement, we have not left Egypt yet. As a people, we were still immersed in the impurity that was Egyptian society. On seder night we are to relive the experience of being saved from spiritual oblivion and as such we are not yet free men when we begin the haggadah.
We omit the blessing at first since we are not yet free. We were so distant from God that we had to be carried out of Egypt by the Almighty himself. Only after reliving the Exodus, and being spiritually revitalised by its retelling, are we free; then we may recite the berachah.