In Catholic belief, Purgatory is an intermediate state between Heaven and Hell, where the souls of sinners who are deserving of punishment, but not eternal damnation, spend a certain amount of time doing penance for their transgression. Eventually, after what may be thousands of years, the souls will be cleansed of their sins, purified, and be allowed to join God in heaven. To use an analogy with the modern justice system, it is like being sentenced to a 20 years in prison, but with the hope of parole, as opposed to life in prison.
These drawings by Dore depict incidents in Dante's fictional account of his trip through Purgatory, as part of his epic journey from Hell to Paradise. It is interesting to contrast the scenes of suffering here, with the incredible torments shown in his drawings for the Inferno or Hell.
Dore's eillustrations of Purgatory do an excellent job of capturing the dual nature of this place. It is a place of suffering, without question, yet unlike Hell, hope remains. No matter how long the sentence, and no matter how long it takes for these souls to be cleaned of their sins, ultimately they will be able to enter Heaven.