Canto 34 of Dante’s Inferno part of Divine Comedy describes Dante and Vergil meeting the three ultimate sinners: Judas, the traitor of Christ, and Brutus and Cassius, who betrayed Caesar.
The pass that Dante is talking about is the gateway to Hell – the Underworld, where the sinners go after their demise. No has ever come from the other side because souls cannot return from Hell – they are dead and buried, and confined to an eternity of punishment for their sins. This is a common motive from myths: a living hero visiting the Underworld and meeting his deceased friends or family there, who, while wishing to return to the realm of the living, can never achieve it. No living person has ever left Hell as Dante is the first to descend there alive – all others, including Vergil, whom he meets there, are dead.
The meaning of these lines lies in the fact that death is inescapable: it cannot be undone, and no one can return from dead until the Doomsday comes. Even on Doomsday, when everyone will be judged for their deeds, and the dead will be revived for the trial, no one will leave Hell to live again. Those who have served their punishment and repented will go to Heaven, while the others will remain in the Underworld to continue their eternal suffering. With these lines, Dante states that there is no way out of death for humanity, and people should accept that and strive to live a life without sin.
Reference
Alighieri, D. (2000). The Divine Comedy. (A. Mandelbaum & S. Botticelli, Trans., E. Montale & P. Armour, Eds.). David Campbell Publishers.