Thomas Aquinas

“ But another man is not competent to exercise this act as principal agent, since neither can he give another man grace whereby sins are remitted, nor can he merit sufficiently, so that he is nothing more than an instrumental agent. Consequently the recipient of the effect of the keys, is likened, not to the one who uses the keys, but to Christ. Therefore, no matter how much grace a man may have, he cannot produce the effect of the keys, unless he be appointed to that purpose by receiving orders. ”

“ Consequently a thing becomes a principal agent through having a form, which it can reproduce in another, whereas an instrumental agent is not constituted thus, but through being applied by the principal agent in order to produce a certain effect. Since therefore in the act of the keys the principal agent by authority is Christ as God, and by merit is Christ as man,* it follows that on account of the very fulness of Divine goodness in Him, and of the perfection of His grace, He is competent to exercise the act of the keys. ”

“ And since it is by appointment of the Church that one man has authority over another, so a man may be deprived of his authority over another by his ecclesiastical superiors. Consequently, since the Church deprives heretics, schismatics and the like, by withdrawing their subjects from them either altogether or in some respect, in so far as they are thus deprived, they cannot have the use of the keys. ”

“ But the remission of sins is the use of the keys. Therefore sinners, who are not "members of the Dove," have not the use of the keys.
Objection 4: Further, the prayer of a wicked priest cannot effect reconciliation, for, as Gregory says (Pastor. i, 11) , "if an unacceptable person is sent to intercede, anger is provoked to yet greater severity." But the use of the keys implies a kind of intercession, as appears in the form of absolution. Therefore wicked priests cannot use the keys effectively.
On the contrary, No man can know whether another man is in the state of grace. ”

“ A character implies the notion of something derived from another, hence the power of the keys which we receive from Christ results from the character whereby we are conformed to Christ, whereas in Christ it results not from a character, but from the principal form. ”

“ The doorkeepers have the key for taking care of those things which are contained in a material temple, and they have to judge whether a person should be excluded from or admitted to that temple; which judgment they pronounce, not by their own authority, but in pursuance to the priest's judgment, so that they appear to be the administrators of the priestly power. ”

“ Further, spiritual grace is hindered by guilt more than by punishment. Now excommunication, suspension and degradation are punishments. Therefore, since a man does not lose the use of the keys on account of guilt, it seems that he does not lose it on account of the aforesaid. ”

“ Kings have no power in spiritual matters, so that they do not receive the key of the heavenly kingdom. Their power is confined to temporal matters, and this too can only come to them from God, as appears from Rom. ”

“ Priests alone have this key, because they alone are ordained for the people in the things which appertain to God directly. The other key reaches to heaven, not directly but through the medium of the Church Militant. By this key a man goes to heaven, since, by its means, a man is shut out from or admitted to the fellowship of the Church Militant, by excommunication or absolution. This is called the key of "jurisdiction" in the external court, wherefore even those who are not priests can have this key, e.g. ”

“ Titus 2:5) , woman is in a state of subjection: wherefore she can have no spiritual jurisdiction, since the Philosopher also says (Ethic. viii) that it is a corruption of public life when the government comes into the hands of a woman. ”