As soon as a coin in the coffer rings, the soul from purgatory springs" —Johann Tetzel, 1465-1519

Mea Culpa is a paradise-and-pandemonium gamer's game that’s all about sins and sinners. Be it at the brothel or at the market, men such as the Pope or the Emperor can be seen hard at work at any time of the day. Even the most miserable miser, though, would be well advised to also strive to get hold of enough precious stones and wine to make sufficient donations towards the Lord's cathedrals. After all, it is through pious generosity that a poor soul can gain the all-important letters of indulgence and be pardoned for a life of greed and lust. When all is said done, what matters is to have sinned just enough to have achieved all goals and gotten away with it, while others took the fall.

In more detail, to win, players have to end the game with their "poor souls" closer to heaven's gate than their opponents. Alas, throughout the game these poor souls pretty much exclusively move in the opposite direction, i.e., towards Hell. Only at the very end of the game might players climb back towards heaven, depending on the letters of indulgence that they managed to collect up to that point.

The accumulation of these letters of indulgence is each player's primary goal. To this end, they take on the roles of different people: the Pope, the Emperor, the Merchant, or the Little Sinner. Each round, these roles in turn grant them access to different special actions. On their turn, players buy or sell goods on the market, visit the brothel to benefit from personal connections, or secretly donate money and goods to the church. Meanwhile, the construction of the game's three cathedrals proceeds. As soon as a cathedral is fully erected, the church will hand out the all-important letters of indulgence. However, only those who have donated the most in either of three categories will actually receive anything.

Many perks that can be used during the game require the players to "sin". Sins are tracked by means of a tally stick and will move the player's poor soul closer to hell. The player who strikes the right balance and picks the right roles at the right time will be able to collect the most valuable letters of indulgence and might stand chance at winning the game. If a player has burdened themselves with too much sin, though, all will ultimately be for naught.