49 The minister of God is a father of souls; and he knows that his toils and his cares cannot adequately be repaid with wealth and honors of earth. He is not indeed forbidden to receive fitting sustenance, according to the teaching of the Apostle: "They that serve the altar may partake with the altar . . . so also the Lord ordained that they who preach the Gospel should live by the Gospel." But once "called to the inheritance of the Lord," as his very title "cleric" declares, a priest must expect no other recompense than that promised by Christ to His Apostles: "Your reward is very great in Heaven." Woe to the priest who, forgetful of these divine promises should become "greedy of filthy lucre." Woe if he join the herd of the worldly over whom the Church like the Apostle grieves: "All seek the things that are their own: not the things that are Jesus Christ's." Such a priest, besides failing in his vocation, would earn the contempt even of his own people. They would perceive in him the deplorable contradiction between his conduct and the doctrine so clearly expounded by Christ, which the priest is bound to teach: "Lay not up to yourselves treasures on earth: where the rust and moth consume and where thieves break through and steal. But lay up to yourselves treasures in Heaven." Judas, an Apostle of Christ, "one of the twelve," as the Evangelists sadly observe, was led down to the abyss of iniquity precisely through the spirit of greed for earthly things. Remembering him, it is easy to grasp how this same spirit could have brought such harm upon the Church throughout the centuries: greed, called by the Holy Spirit the "root of all evil," can incite to any crime; and a priest who is poisoned by this vice, even though he stop short of crime, will nevertheless, consciously or unconsciously, make common cause with the enemies of God and of the Church, and cooperate in their evil designs.
Source: Ad Catholici Sacerdotii (Vatican.va)