Reciting a Blessing on the Haggadah

[From Rabbi Shlomo Aviner's Commentary on the Haggadah]

Question: Why didn't our Sages establish a blessing on reciting the Haggadah, "Who has sanctified us with His commandments and commanded us regarding the Haggadah"? The basis of reciting the Haggadah after all is a Torah mitzvah, counted among the 613 commandments, as the Rambam writes: "To relate the miracles and wonders that were performed for our ancestors in Egypt on the night of the fifteenth of Nisan" (Rambam, Hilchot Chametz U-Matzah 7:1).
Answer: Many answers have been suggested for this question:
a. The Rosh wrote: "And regarding the question of why we do not recite a blessing on reciting the Haggadah, The Holy One, blessed be He, commanded us to perform many acts as a remembrance of the Exodus and we do not recite a blessing on them." According to his opinion, there is not an independent mitzvah to recite the Pesach Haggadah. Only if someone asks you about the Exodus must you explain it to them, but if no one asks, there is no need to say anything. In such a case, you perform all of the acts of that night, i.e. eating matzah, etc…, and through these acts you will remember the Exodus. A difficulty on the Rosh's position: It is written in the Mechilta (a text which derives laws from the Torah) that even if no one asks you, you are still obligated to relate the story of the Exodus. A rejection of this difficulty: The Rosh explains that the Mechilta is discussing a rabbinic obligation, but connects it to a verse in the Torah.
b. The responsa "Besamim Rosh" explained that we do not recite a blessing on blessings and praises, just as we do not recite a blessing on the Birkat Ha-mazon (the blessing after eating). The Haggadah is composed entirely of praises. A difficulty on the position of the "Besamim Rosh": We recite a blessing on Hallel even though it is filled with praises.
c. Rabbenu Yerucham: The blessing on the Haggadah is included in Kiddush when we say, "a remembrance of the Exodus from Egypt."
d. Rashba: We do not recite a blessing since this is a mitzvah which has no known limit. One can fulfill his obligation with one statement, and the more he relates the story of the Exodus, the more praiseworthy he is.
e. The Meiri: We do not recite a blessing since after we recited the Shema in Ma'ariv, we said "Emet Ve-emuna – True and Faithful" which ends "Blessed are You, Hashem who redeemed Israel," and this serves as the blessing. A difficulty on the last three answers: Since the mitzvah is reciting the Haggadah and relating the story of the Exodus, we do not fulfill our obligation by recited Kiddush or with a mere statement.
f. Shibulei Ha-leket: The blessing on the Haggadah is the blessing we recite before eating the matzah, which begins '"Who has redeemed us." The Rabbis placed this blessing at the end of relating the Exodus, since if we said "Who has redeemed us" at the beginning of the Seder, we would not go back and discuss the enslavement.

There are additional explanations. The Meiri actually quoted an opinion that we do recite a blessing at the beginning (See Ha-Moadim Be-Halachah by Rav Shlomo Yosef Zevin, p. 279 and Talmudic Encyclopedia vol. 8, p. 179).