Many mainline Christians and Christian churches reach back beyond church tradition into the days of the ancient Israeli people who celebrated the first passover. Scheduling the traditional seder meal is a quasi-historical, quasi-religious experience for non-Jewish participants. As someone who loves the idea of experiencing different religious traditions, I think that this is great. But, I also believe that due respect must be shown to the religious order. For example, a non-Catholic shouldn't partake of the eucharist in the Catholic Church.
The original Passover is discussed in Exodus 12 and it includes this command: "Then the Lord said to Moses and Aaron, “These are the instructions for the festival of Passover. No outsiders are allowed to eat the Passover meal." Exodus 12:43.
No outsiders!? How can this foster diversity and agreement among the world's people today? Well, frankly I don't know. I understand the reason why this would remain true: Passover is a Jewish High Feast. Like the Sabbath, no work is to be done on those days and preparing the seder for a non-Jew would not be a necessity (and thuse in violation of other rules of Jewish orthodoxy).
So, I can understand the logic of following Exodus 12:43. I haven't been invited to celebrate a seder with any of my Jewish friends; so maybe this tradition remains alive? (Interestingly, a Google search reveals that outsiders are often invited to family Seders.) If and when I'm invited, I'll have to figure this out!
For those that are wondering, the Seder will be served this year on April 5. Why am I posting this now? (1) Fishing for an invite and (2) I read Exodus 12 last night as part of my Bible-in-a-Year (going strong!).