In the following passage from Act 1, Prometheus angrily curses Jupiter, using simile as a means of describing Jupiter's soul:
What ruin
Will hunt thee undefended through the wide Heaven!
How will thy soul, cloven to its depth with terror,
Gape like a Hell within!
In order to emphasize the extent of his suffering and his just craving for retribution, Prometheus states that Jupiter’s soul will “Gape like a Hell within”—a phrase that is self-evidently ironic, on account of whom Prometheus is addressing. Particularly in a Christian context, a soul is traditionally regarded as inherently sacred. It is situationally ironic, then, given Shelley's context, that Jupiter, as a god who lives in the sacred realm of heaven, would have a soul that gapes "like a hell within."
While Jupiter is no pillar of morality within the Greek and Roman myths, the God of Christianity is supposed to be utterly holy, with no hellish soul or sinful misdeeds in sight. To imply that God is impure or immoral in Christianity would be heresy; in Greek and Roman mythology, however, it was not uncommon for gods to act immorally. Jupiter, for instance, was known to frequently cheat on his wife, siring demigods with an untold number of mortal women. In Prometheus Unbound, Shelley blurs the lines between so-called "heathen" religions and Christianity, muddying the waters in terms of how to regard godly morality.
