I came across a sermon from Johann Tetzel, the indulgence peddler who provoked Luther’s 95 Theses. Part of his sales pitch had to do with the popular, though unofficial, teaching that Christians must suffer 7 years in the fires of Purgatory for each sin they have committed. Doing the math reminds us of what it was like to be a western Christian in 1516.
Though Christ died for the sins of the world, according to classic Roman Catholicism, His sacrifice erases the penalty for original sin and for sins committed up to the time of Baptism. After that, Christians have recourse to the penitential system to deal with their sins. Catholics believe that even Christians can go to Hell, if they commit mortal sins. These can be forgiven, though, through the sacrament of Reconciliation, involving private confession before a priest, acts of penance, and absolution. That removes the eternal punishment that the sin deserves. But all sins, including the more minor venial sins, require temporal punishment. Earthly suffering can count for this, but most of the temporal punishment–which is necessary even for sins that have been forgiven–happens after death in Purgatory.