Gregory the Great — as excerpted in the Catena Aurea on Luke 19:45-48

“(ut sup.) Mystically, such as the temple of God is in a city, such is the life of the religious in a faithful people. And there are frequently some who take upon themselves the religious habit, and while they are receiving the privilege of Holy Orders, are sinking the sacred office of religion into a bargain of worldly traffic. For the sellers in the temple are those who give at a certain price that which is the rightful possession of others. For to sell justice is to observe it on condition of receiving a reward. But the buyers in the temple are those, who whilst unwilling to discharge what is just to their neighbour, and disdaining to do what they are in duty bound to, by paying a price to their patrons, purchase sin.”