The last supper in the gospels has strong associations with the Passover seder. However, it has very little to do with either component of the biblical Passover in Exodus 12. What happens to Passover after the biblical period? Biblical ritual practice changes dramatically with the destruction of the temple in 70 CE. Without the temple, there is no place to sacrifice offerings. Eating ritual meals akin to ritual offerings are possible though, so a meal like that described in Exodus 12 is a way to participate in the festival without the temple. The Passover now occurs in the household, with highly symbolic elements in the meal itself as well as in the practice of commemorating the event. And today, the Passover seder also involves a ritual re-telling of the Exodus narrative and retains the symbolic meal. The elements of Passover that were domestic in nature were easily maintained, even if there is now confusion as to why these complicated processes are ritually done when they are.
The rise of rabbinic Judaism predates the destruction of the temple, so the interpretation of ritual outside of temple-based sacrificial acts was already present. The seder is very much based on Graeco-Roman meal practices; however, many parts of the modern seder are symbolic (four glasses of wine, four questions, four children who are told the story), and elements of rabbinic material, mostly from the Mishnah (2nd century CE). The narrative and storytelling elements are now central to the practice of the modern Seder.
By the thirteenth century, folk songs entered Passover traditions without explanation or religious reasoning. Likewise, modern liberal seders incorporate new elements in order to innovate within the confines of the ritual, to be inclusive of marginalized communities that are “as unwelcome as an orange on a seder plate.” At the heart of most rituals, and Passover is no exception, is an ongoing dynamism.