The Passover meal described in Exodus centered on a lamb, slaughtered at twilight and roasted whole, its blood marking the doorposts of the Israelite houses in Egypt. For as long as the Jerusalem Temple stood, this remained a sacrificial rite: families brought a lamb to the Temple to be slaughtered by priests before eating it that night, a practice ancient sources outside the Bible also describe.
The Temple's destruction in the year 70 removed the sacrifice itself, and it was the rabbis of the following two centuries, compiling what became the Mishnah tractate Pesachim, who built the Seder as it survives today around that absence: wine, unleavened bread, bitter herbs, and a script of questions and answers that turns the missing lamb into an occasion for retelling rather than eating.
The Haggadah, the text read at the table, is not itself biblical; its core dates to the rabbinic period, but it kept absorbing material for over a thousand years, including medieval poems, the song Chad Gadya, and modern additions such as an orange on the Seder plate or a cup for Miriam, symbols added in the twentieth century to mark concerns the older text does not address. Reform, Conservative, and Orthodox households today can use Haggadah texts that differ substantially in content and length while calling the result by the same name.