So okay we go to space. Meet another starfaring civilization, we come in peace, diplomatic exchange and all that trekkie shit. We begin to exchange information about our cultures, study one another's history and art, humans fall in love with their form of culinary immersive theater (fortunate that we have relatively compatible digestive apparati), aliens are inexplicably apeshit about the works of Frank Perry. Everything is proceeding normally or as close as first contact can come to "normal" until at one of the shared meals that's beginning to become routine a midrank alien crewmember starts apologizing profusely.
"I see this dish contains potatoes and I fear I must request an alternative from the cook. I mean no offense! I cannot partake, in memory of my ancestors."
This causes some confusion among the human crew, who have observed the aliens—indeed, this particular one—expressing their appreciation of Earth's most masterfully bioengineered tuber. After some discussion, it becomes clear that the prohibition is not universal, but only applies for a span of several days as a way of honoring an ancient tale of a narrow escape in haste, during which only unripe tubers could be harvested.
Not without grumbling from the kitchen crew, the alien is served a meal devoid of root vegetables. The meal continues without further event, as the humans try with limited success to explain the plot of Mamma Mia! to a species with a five-stage reproductive cycle and four distinct terms that all roughly mean "parent".
After the meal, though, Ensign Schwartz nervously approaches the potato-averse alien and asks for more details on this ancient story. Always happy to tell a story, the alien explains that their ancestors were held in suffering and bondage by a great empire until their deity raised up one of their own as a great prophet. This prophet demanded freedom from the emperor and the deity rained down retribution each time freedom was refused, culminating in the death of each first-brood hatchling of the oppressor's people. Seeing this death, the emperor granted the people permission to leave, which they did (as explained) in great haste.
And that's how Ensign Reuven Schwartz discovered the principle of Universal Judaism.
As more and more species connected, it happened again and again. The details were always different, accommodating differences in biology, geography, and history, but the broad points were consistent: a covenant, oppression, deliverance, wandering, a promised land, and finally diaspora. Among no species did this religion represent more than a small fraction of its population, but everywhere it existed it had its book.
