In the times of the Temple, there were two opinions on how to eat the substitution for the sacrificial lamb. The majority ruling was to eat the Matzah, Maror and Charoset separately, yet Hillel believed that they should be eaten all together. In order to compromise with each other, they created a section within the Seder for the Matzah and Maror to be eaten separately, and a section in the Seder for them to be eating together as a whole.

haggadah Section: Koreich