Theophanies of the Ancients

[The Gods] judged impure men to be unworthy of their sight, and consequently they were unwilling to appear to them. This can be gathered from Euripides in the Bacchae, line 502, where Bacchus is recorded as not having been revealed to Pentheus—even though Bacchus was present—on account of Pentheus's remarkable wickedness: "But you yourself, being impious, do not see [him]." original Greek: Σὺ δὲ ἀσεβὴς αὐτὸς ὤν, οὐκ εἰσορᾷς. The Latin translation provided in the text is: Tu uero ipse impius existens, (Bacchum) non uides. Hence, those to whom it was not permitted to gaze upon the Gods in their presence were held to be impious and base, as Callimachus excellently teaches in his Hymn to Apollo, line 10:

"He who does not see [Apollo] is lowly. We shall see you, Apollo, and we shall never be lowly."
original Greek: ὅς κέ μιν ἴδῃ, λιτὸς ἐκεῖνος. Ὀψόμεθ’ , ὦ ἑκάεργε, καὶ ἐσσόμεθ’ ἄποτε λιτοί. The Latin translation provided is: Qui non uidet (Apollinem) abjectus ille est. Videbimus te, Apollo, & nunquam erimus abjecti. Note that the Greek text generally implies that seeing the god makes one great, while not seeing him marks one as lowly.

For "it is not lawful," as is Plato's axiom in the Phaedo, page 67, "for the impure to touch the pure." original Greek: μὴ θεμιτόν ἐστιν ... μὴ καθαρῷ καθαροῦ ἐφάπτεσθαι. Latin: fas non est, impuro contingere purum. The reason was obvious: namely, that the divine purity and sanctity of the Numina Latin for divine powers or spirits; the essential essence of a deity were believed to be equally harmed and violated by profane eyes and by an illicit and impious gaze.

Th. 8.

Occasionally, however, it happened that even impious and impure men saw the Gods in their presence; but this was joined with the greatest and most immediate loss and danger to them. For they did not carry this away without punishment, but were penalized either with madness, or blindness, or other calamities, such as being suddenly changed in form This refers to metamorphosis, a common theme in Greek mythology where humans are transformed into animals or plants as punishment.. The same thing happened to those who gazed upon the Gods against their will. To this refers a passage of Callimachus in his Hymn on the Bath of Pallas, line 100 and following:

"The laws of Cronus The father of Zeus and ruler of the world in the Golden Age speak thus: Whosoever beholds any of the immortals, when the God himself does not choose it, sees him at a great price."
original Greek: Κρόνιοι δ’ ὧδε λέγοντι νόμοι, Ὅς κέ τιν’ ἀθανάτων, ὅκα μὴ θεὸς αὐτὸς ἕληται, Ἀθρήσῃ, μισθῷ τοῦτον ἰδεῖν μεγάλῳ.