Ubik (1969) is a science fiction novel by Philip K Dick. Without summarizing the plot, or giving away the punch line; suffice to say that it depicts an evil-permeated and rapidly entropic world, which is opposed by a 'god' who is excluded from all mainstream and normal ways of communicating and helping.
In this world, The System is all-pervasive. God's messages must come from peripheral and unexpected directions in order to get past the monitoring intelligence. Good can only work indirectly. "God" is to be found only in the "trash" of this culture.
We might imagine an equivalent for our world, in which the real Christian needed to disguise itself as trash, and move out to the places into which The System does not (yet) extend. It can only find an outlet among the despised people, those regarded as absurd, insignificant - or labelled by The System as insane, idiotic, evil...
The System fights back by mimicking the secret divine messages by deploying fakes as bait... The System pretends that these people and messages are radical, anti-Establishment, or disapproved; yet The System contrives to draw attention to them, nonetheless.
The System advertises (under pretense of warning against) exactly these baited traps; which it hopes will be mistaken for divine messages - but will lead back into The System.
Meanwhile, the real messages from the divine, real goodness, are unknown or unnoticed except to those who honestly seek them, and are sensitized to their truth.
The System is entropic, parasitic, destructive - and opposed to The System is Ubik.
Ubik is found in various trashy forms, such as an aerosol that (albeit temporarily) opposes and reverses entropy; it heals the dissolutions of The System.
Ubik is, indeed, understandable as an allegory to the Eucharist; the bread and wine of the Mass as it is supposed ideally to function; yet which is but a "momentary stay against confusion" (to use Robert Frost's description of poetry).
Even if it was available in unlimited supply and on-demand (and, in PKD's story as in our world, Ubik is actually difficult and dangerous to locate, and has a short 'shelf life'); Ubik does not provide a permanent answer, as does Not the Eucharist.
But Ubik provides a chance to break free from the constancy of destruction by the entropy of the world -- a chance, perhaps, to clear our thoughts and make further enquiries; to seek and discover the availability of a permanent - an eternal - solution to entropy
To discover how to reach a world without entropy, without evil.