Here is what it was like to be a believing Christian five hundred years ago. The church did teach that Jesus Christ, the incarnate Son of God, bore the punishment for our sins and died for the forgiveness of our sins. It taught that the redemption that Christ won had to be dispensed by the church.
What this meant in practice was that Christ’s death, applied through baptism, was thought to free us from original sin. Sins committed after baptism had to be dealt with in a different manner. The Roman Catholic Church still teaches that Christians can be damned if they commit mortal sins. But these can be forgiven if the sinner feels contrition, confesses them to a priest, performs an act of penance, and receives absolution. Thus, the sins are forgiven, in the sense that they no longer will incur eternal punishment. But they will still incur temporal punishment.
This happens in purgatory. After death, Christians must be punished for the sins they committed on earth. This is necessary before the Christian may enter heaven. Purgatory was a realm of fire. Sinners burn in purgatory, much as they would in hell, though these pains are only temporary. But suffering the fires of purgatory might last thousands of years.
This is what believing Christians have to endure, for sins for which they have repented and found forgiveness, that the church admits were atoned for by Christ, and that were confessed and absolved.
But God, by His grace, can reduce this time, the Roman Catholic Church says. This is why we must pray for the dead, that God would remit their penalty. Also, the church can reduce this time by means of the “treasury of merit.” The saints—defined as someone found to be already in heaven, their time shortened by God’s special grace and the holiness of their lives—have more merit than they need to enter heaven. So the church can transfer that extra merit to living Christians or to the dead already in purgatory. These are indulgences.
The church granted—and still grants—indulgences for various acts of devotion, such as venerating relics or going on a pilgrimage. And then, at the start of the Reformation, the pope was selling them.
Imagine the horror of believing that after death, for all of your piety, you would experience thousands of years of penitential fire. But imagine the relief if for a week’s wages2 you could buy a plenary or complete indulgence and go straight to heaven. And if you could raise another week’s wages, you could free your dead child.
