The Original Sin
Every major culture under the Manifold Sky shares remants of an ancient and half-forgotten mythology surrounding what came before - a hazy ancestral recollection of an antideluvial time where people resided in places where the horizons stretched forever in all directions before curving away, lit by celestial bodies that crossed the skies in their courses. This mythical epoch is known by many names in many languages, but one appelation has come to be accepted by most: The Curved Time.
The very oldest religious texts speak nebulously about some kind of great 'sin' that was committed, and that this sin greatly displeased some greater spiritual power to the extend that this power imprisoned the peoples of The Curved Time within the Manifold as punishment. Though all cultures know something of The Curved Time, speculation runs rampant when it comes to the question of what the specific nature of the sin was that brought The Curved Time to a close. This question of 'original sin' has bedeviled theologians and philosophers for countless generations.
Cultural Reception
Taboos about performing 'magic' beyond what a religious traditions already allows are sometimes thought of as stemming from whatever the 'original sin' was. Divination by Vyozha in the Church of the Unexpected or the use of Ritual Sigils in Rostran Esotericism would not count, but violations of the natural order - like trying to create an ixulova tun - might. Hubris, lust for power, and great violence are also considered to have been elements of the sin, and most extant philosophies thus make a point of discouraging these behaviors - with perhaps the exception of Ixa Ad-Korvidiu - in case those committing these sins might somehow make things worse.
In Literature
The Incunabula of the House of the Unexpected frames the Unexpector deities like correctional officers for the gaol that is the Manifold, explaining that they offer mercy and, in time, liberation from the travails of temporal existence in exchange for obeyance towards their respective virtues. Universal Artifice, a holy text of Forgism, addresses the sin but takes a more fatalistic approach to being trapped within the Manifold, stressing that recognizing the world as facade offers peace but does not shorten one's sentence within it. The Ixaba takes a still different approach towards the sin and, though acknowleding its existence, does not deny that something like it will inevitably happen again; for Esotericists, The Curved Time is less a place than a time, a single epicycle in the grand order of the cosmos, and so it is better to forestall the coming of a new sin through piety and virtue than to waste time running from the previous one.
Related Organizations
I like the way you've woven this concept into the different religious sects of your world.