Ezekiel 40:46

"And he said to me: This is the treasury that faces the southern way of the priests, who keep watch in the temple's guardrooms. Furthermore, the treasury that faces the way of the north will be for the priests who serve at the altar: these are the sons of Zadok who come near from the sons of Levi to the Lord, to minister to Him."

There are moreover priests of a lesser order who keep watch for the ministry of the altar, who namely investigate carefully the sins of those who transgress in aid of their superiors, and correct the life of carnal men, and bring them to the point where through the laments of penance they set ablaze, as it were, the flesh in sacrifice which they had previously permitted to live in sin. For those who preside over the holy Churches are not able to do all things by themselves. But while they themselves are occupied with spiritual matters, if any wicked and carnal deeds are committed, they entrust these to others to be examined and corrected. Through whom, when the carnal life is corrected and those making progress arrive at the pursuit of abstinence and prayer, the flesh is now set ablaze, as it were, upon the altar, so that in the sight of the almighty Lord a sacrifice may give forth fragrance from that very source whence formerly sin was displeasing.

But concerning both orders of priests it is added: These are the sons of Zadok, who approach from the sons of Levi to the Lord to minister to Him. Zadok in Latin means just. But who is just, except Him to whom it is said: You are just, Lord, and Your judgment is right? And who are the sons of the just, except those of whom it is written: But as many as believed in Him, He gave them power to become sons of God? Now Levi is interpreted as taken up. But who has been taken up by the Lord, except the faithful people, who through the sacraments of faith have been separated from the faithless? Therefore all who perseveringly devote themselves to spiritual activities are sons of the just. And from the sons of the people taken up they approach the Lord to minister to Him, because from those same faithful ones are chosen those who come to the ministry of almighty God and devote themselves to heavenly studies for the instruction of the people.

But we must carefully inquire who those are who minister to the Lord. For not all who read, not all who preach, not all who give of their own possessions, not all who chastise the body through abstinence of the flesh, minister to the Lord. For those who by reading and preaching seek their own glory, by giving away what they have and wasting the body in abstinence, desire to receive praises from men, minister to themselves, not to the Lord. Against which the Lord says through the Psalmist: "He who walks in the immaculate way, he ministered to me." For he has a stain on the way who in the good work he does sets before himself the reward of earthly glory, who seeks to receive his reward in this world, and defiles in the sight of God the appearance of the good work with the stain of depraved intention. For perhaps someone intent on the pursuit of discipline burns with zeal, cuts off the faults of offenders, yet if he is led to do these things not from love of almighty God but by his own zeal, in these matters he ministers to himself, not to the Lord. Another, lest he seem harsh, tolerates gently many things that are wickedly perpetrated. This one therefore, because he does not wish to be seen as severe for the Lord, through his pursuit of leniency ministers to himself, not to the Lord. It remains therefore that whether we labor in the ministry of the word, or give our goods to the needy, or tame the flesh through abstinence, or are moved by zeal, or sometimes gently tolerate evil things through patience, we must most carefully examine our intention, so that everything we do, we do not with our own zeal but the Lord's, lest in those things we do we minister rather to ourselves than to the Lord. […]

But in this matter a question arises, since it was said above that the treasury chambers had their fronts toward the Southern way, by what reasoning is it now said that the treasury chamber which looks toward the southern way belongs to the priests who keep watch in the guardianship of the temple, and the treasury chamber which looks toward the way of the North belongs to the priests who keep watch at the ministry of the altar.