Philological Dissertation on Honored, Learned, Adored, and Fruitful Virginity

...was later loved by Metiochus the Phrygian, but having cut her hair, she decided to appear unadorned, then went to the Campanians and lived there. Perhaps for this reason, Dionysius called her chaste. Naumachius, in Stobaeus, also has excellent things in praise of Virginity, and Aelian in Various History, Book 13, Chapter 1, perì Atalantēs concerning Atalanta.

But this is most relevant to our purpose: that in the most famous temples of almost all nations, there were Virgin priestesses, not only prophētides prophetesses for delivering oracles (about which there is no doubt, except that a little later not only Virgins were admitted to that office), but also for guarding the temples and performing sacred rites, or for sanctioning perpetual Virginity; besides the fact that such sacrifices were most acceptable to the Gods.

Regarding Vesta, the matter is more manifest than to need proof. Lipsius, in his treatise on Vesta and the Vestals, reports from Plutarch that in Greece, in Athens, in Delphi, and wherever eternal fire is kept, there presided, if not Virgins, at least widows, and those chaste from men: but for the most part, and from ancient times, they were Virgins.

Ovid gives the reason for this, that a Virgin is sterile just as fire is, Fasti, 6:

Nor do you understand Vesta as anything other than living flame,
And you see no bodies born from flame.
Rightly, therefore, is she a Virgin who sends back no seeds,
Nor receives them, and loves the companions of Virginity.

Ovid himself has another reason elsewhere,