Why would anyone want to buy a church office?
In theory, church offices (salaried positions in the Catholic Church hierarchy) went to spiritually deserving individuals who had earned the office by virtuous deed on the church's behalf; in actuality, they were "bought" by unscrupulous wealthy men whose only interest was in the power and additional wealth the offices generated. While we like to think of the Church as a religious force, in the Middle Ages it was a political monolith interested mainly in earthly power. Dante has condemned these charletons to their own special ring in Hell. A modern parallel would be a rich businessman who, through bribes and contributions to political campaigns, "bought" a plum position on a committee or staff of someone in public office, for the sole purpose of generating more wealth, not to serve the constituents.