The Haggadah is the text recited at the Passover seder, and its whole structure is shaped by a single obligation: to tell a child what happened when Israel came out of Egypt.
Telling as commandment
The Torah commands that the story of the deliverance be told to the next generation, and the Haggadah is the fulfilment of that command, built around the questions a child asks and the answers given, so that the retelling is framed as instruction across the generations. The text is arranged as a commentary on a short scriptural declaration about the Exodus, expanding it with narrative, discussion, psalms and song, and it directs the actions of the seder, the eating of the symbolic foods, the drinking of the cups, the questions and the explanations, so that the book is a script for the evening rather than a book to be read straight through.
Many Haggadot
Because it is a domestic and much-loved text, the Haggadah has been copied, printed and illustrated more than almost any other Jewish book, and it exists in a vast number of versions, from richly illuminated medieval manuscripts to editions produced by every community and movement, so that families keep and cherish particular Haggadot. Its combination of fixed core and endless local addition has made it a mirror of Jewish life across time and place. The book is inseparable from the seder plate whose foods it explains, the two together carrying the observance of the night on which the founding story of the people is retold.