The River Acheron
"In ancient Greek mythology, Acheron was known as the river of woe, and was one of the five rivers of the Greek underworld. In the Homeric poems the Acheron was described as a river of Hades, into which Cocytus and Phlegethon both flowed.
The Roman poet Virgil called it the principal river of Tartarus, from which the Styx and Cocytus both sprang.The newly dead would be ferried across the Acheron by Charon in order to enter the Underworld.
"Charon stands on the gunwale of the boat"
In Greek mythology, Charon or Kharon (// or //;Greek Χάρων) is the ferryman of Hades who carries souls of the newly deceased across the rivers Styx and Acheron that divided the world of the living from the world of the dead. A coin to pay Charonfor passage, usually an obolus or danake, was sometimes placed in or on the mouth of a dead person. Some authors say that those who could not pay the fee, or those whose bodies were left unburied, had to wander the shores for one hundred years.
"A lighter vessel must bear thee" implies that Dante (and/or) Virgil will escape Hell and perhaps make Purgatory.
"Purgatory, according to Catholic Church doctrine, is an intermediate state after physical death in which those destined for heaven "undergo purification, so as to achieve the holiness necessary to enter the joy of heaven".[ Only those who die in the state of grace but have not in life reached a sufficient level of holiness can be in Purgatory, and therefore no one in Purgatory will remain forever in that state or go to hell. This theological notion has ancient roots and is well-attested in early Christian literature, but the poetic conception of Purgatory as a geographically existing place is largely the creation of medieval Christian piety and imagination.
"Methodist churches hold that "the Romish doctrine concerning purgatory ... is a fond thing, vainly invented, and grounded upon no warrant of Scripture, but repugnant to the Word of God. Its founder John Wesley believed that there is "an intermediate state between death and the final judgment, where those who rejected Christ would be aware of their coming doom (not yet pronounced), and believers would share in the 'bosom of Abraham' or 'paradise', even continuing to grow in holiness there. Methodism does not formally affirm this belief, but maintains silence on what lies between death and the last judgment."