The Book of the Three Dwelling-Places
By Saint Patrick
About the infernal punishments.
There are two principal torments in Hell: unbearable cold and the heat of inextinguishable fire. For this reason, it is said in the Gospel, "In that place, there will be wailing and grinding of teeth" (Matthew 13:51, 22:13 and 25:50). For wailing and melting of the eyes comes from heat, and surely grinding of teeth comes from cold. Hence, also the blessed Job says, "They will pass from the waters of snows into extreme heat" (Job 24:19). Numberless punishments are exacted through these two torments, as you can see: intolerable thirst, the punishment of hunger, the punishment of stench, the punishment of horror, the punishment of fear, the punishment of anguish, the punishment of darkness, the severity of the torturers, the presence of demons, the ferocity of beasts, the barbarity of the rulers, being torn apart by immortal vermin, the worms of conscience, the fire of tears, the sighs, the misery, the grief without a remedy, the unbroken chains, eternal death, punishment without end, the absence of Christ after the vision of him (which is called the greatest thing above all others), and all the other intolerable punishments.
Concerning the absence of Christ as a punishment in Hell, some manuscripts have quoad ("inasmuch as", "with respect to") where the word post ("after") appears. In both variants, the punishment is the same: the absence of Christ in general, and the Beatific Vision in particular.
The use of the word "after" indicates that the people in Hell have seen Christ, and they were afterwards thrown into Hell. This could be applied to humans who have seen Christ during his second coming in glory (which is a precursor to the Beatific Vision). Saint Augustine specifically applies this to Satan and his demons, who had the fullness of the Beatific Vision, but still denied God. The author's point is clear: Because the Beatific Vision is the greatest of all things, the loss of the Beatific Vision causes more regret than losing any other thing. However, because humans are more inclined to regret the loss of good things than demons are--demons tend to rejoice at the loss of good things--this punishment has a greater impact on the humans in Hell.
As the author discusses in later chapters, the absence of Christ is a double punishment. It is not the case that the people in Hell have only one regret: having Christ, then losing him. They also regret the fact that--right now--they are separated from Christ. In other words, they regret both their past separation from Christ and their present separation from Christ. Doubtlessly, if they ever think about the future, they regret their future separation from Christ. But they are probably more inclined to regret their past, not their future, because it was in the past that they became separated from God through their sins. Sin separates us from God and God's transforming love; let us never foolishly choose to follow after sin instead of God.