Final answer:
Indulgences were claimed to reduce the punishment for sin after death by reducing time in purgatory. This practice became controversial, contributing to the Protestant Reformation and Martin Luther's critique, asserting that true repentance and faith were necessary for remission of sins.
Step-by-step explanation:
The practice that was claimed to release you from all or part of the punishment for sin was the purchase of indulgences. Indulgences were essentially a way to reduce the time spent in purgatory after death. When a person died, they were believed to go to purgatory to atone for their sins unless those sins had been already forgiven and the penalties for them satisfied in life. Indulgences could be obtained through actions of religious merit or donation to the church, and they reduced or cancelled the period of purification in purgatory.
In the medieval church, this concept became especially prominent. It was believed that indulgences drew on the 'treasury' of merit accumulated by Jesus Christ and the saints, a surplus of virtuous acts that the Pope could transfer to a living or deceased person. This practice was a significant source of income for the church but became a point of contention leading to the Protestant Reformation, majorly sparked by Martin Luther's disapproval of the sale of indulgences, as seen during the Johann Tetzel affair.