"[I]ndulgences served not merely to dispense the merits of the saints but also to raise revenues. They were the bingo of the sixteenth century. The practice grew out of the crusades. At first indulgences were conferred on those who sacrificed or risked their lives in fighting against the infidel, and then were extended to those who, unable to go to the Holy Land, made contributions to the enterprise. The device proved so lucrative that it was speedily extended to cover the construction of churches, monasteries, and hospitals. The gothic cathedrals were financed in this way. Frederick the Wise was using an indulgence to reconstruct a bridge across the Elbe. Indulgences, to be sure, had not degenerated into sheer mercenariness. Conscientious preachers sought to evoke a sense of sin, and presumably only those genuinely concerned made the purchases. Nevertheless, the Church today readily concedes that the indulgence traffic was a scandal, so much so that a contemporary preacher phrased the requisites as three: contrition, confession, and contribution."
(Chapter IV, Onslaught, p. 72)