They advance Luther's positions against what he saw as abusive practices by preachers selling plenary indulgences, which were certificates which would reduce the temporal punishment for sins committed by the purchaser or their loved ones in purgatory.
They advance Luther's positions against what he saw as abusive practices by preachers. These preachers are selling plenary indulgences. Plenary indulgences were certificates. These certificates would reduce the temporal punishment for sins. These sins are committed by the purchaser in purgatory. These sins are committed by their loved ones in purgatory.