John Keats' "Ode to Psyche," written in 1820, looks back to a myth from a much earlier time. The Roman author Apuleius, writing some 1700 years earlier, tells the love story of Cupid and Psyche in his Metamorphoses. In the first half of Keats' poem, he laments that Cupid's beloved Psyche did not have many of the things that accompanied a woman of her beauty, even though she was more wondrous than any goddess. Among other things, Keats notes that Psyche had

No shrine, no grove, no oracle, no heat
Of pale-mouth'd prophet dreaming.

Keats, who has discovered his own "Psyche," realizes that his beloved faces a similar situation, so he offers to be

Thy shrine, thy grove, thy oracle, thy heat
Of pale-mouth'd prophet dreaming.

Given the oracular context of these lines (shrine, grove, oracle, prophet), it would appear that Keats has in mind Apollo's oracle at Delphi and the priestess (known as the Pythia) who served as the spokesperson for Apollo. The reference to the pale mouth makes me think that Keats is thinking of the Pythia, because a woman in ancient Greece would be more likely to have fairer skin than a man, who spent most of his time outdoors (women spent most of their time indoors and thus out of the sun).

When the Pythia delivered Apollo's prophecy, she is usually said to have been in some sort of trance (hence Keats' reference to "dreaming"). The "heat" may refer to the frenzy that was also supposed to come upon the Pythia when the spirit of Apollo fell upon her.