Dante Alighieri

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"Lasciate ogni speranza, voi ch'intrate."
- Translation: "Abandon all hope, whoever enters here."
- Source: Inscribed above the gates of Hell (Inferno III:9).
"Il gran rifiuto."
- Translation: "The great refusal."
- Source: The decision of to abdicate the Papacy and allow Dante's enemy, , to gain power (Inferno III).
"L'amor che move il sole e l'altre stelle."
- Translation: "The love which moves the sun and the other stars."
- Source: Dante's final vision in the Divine Comedy (last line of Paradiso XXXIII).

"The hottest places in hell are reserved for those who in times of great moral crisis maintain their neutrality", or a variation on that.
Source: Probably John F. Kennedy [1]. (Dante placed those who "non furon ribelli né fur fedeli" — were neither for nor against God, such as Celestine V, above — in a special region near the mouth of Hell; the lowest part of Hell, a lake of ice, was for traitors.)