I am trying to work out why the Catholic church was selling indulgences in the run up to the reformation. I am under the impression an indulgence is in crude terms to "have your sins forgiven and get out of purgatory". Is this not very similar to Sacrament of Penance / confession which I assume was free?
These seem to cover very similar ground. What was the difference between them? Why was one free and one paid for?
Well, Confession is having your sins absolved, that is, return to a state of grace and avoid a path leading to damnation. A reconciliation, if you will. But there is still a need to make up for the consequences of sin, most notably the offense the penitent has caused to God. Now ordinarily this is achieved after the death of the penitent in Purgatory. But this can also be done by doing pious works or actions, which are indulgenced, and commute this reparation, in whole or in part. That is an indulgence.