I answer that, By sin, man loses a twofold dignity, one in respect of God, the other in respect of the Church. In respect of God he again loses a twofold dignity. one is his principal dignity, whereby he was counted among the children of God, and this he recovers by Penance, which is signified (Lk. 15) in the prodigal son, for when he repented, his father commanded that the first garment should be restored to him, together with a ring and shoes. The other is his secondary dignity, viz. innocence, of which, as we read in the same chapter, the elder son boasted saying (Lk. 15:29): "Behold, for so many years do I serve thee, and I have never transgressed thy commandments": and this dignity the penitent cannot recover. Nevertheless he recovers something greater sometimes; because as Gregory says (Hom. de centum Ovibus, 34 in Evang.), "those who acknowledge themselves to have strayed away from God, make up for their past losses, by subsequent gains: so that there is more joy in heaven on their account, even as in battle, the commanding officer thinks more of the soldier who, after running away, returns and bravely attacks the foe, than of one who has never turned his back, but has done nothing brave."
By sin man loses his ecclesiastical dignity, because thereby he becomes unworthy of those things which appertain to the exercise of the ecclesiastical dignity. This he is debarred from recovering: first, because he fails to repent; wherefore Isidore wrote to the bishop Masso, and as we read in the Distinction quoted above (Objection [3]): "The canons order those to be restored to their former degree, who by repentance have made satisfaction for their sins, or have made worthy confession of them. On the other hand, those who do not mend their corrupt and wicked ways are neither allowed to exercise their order, nor received to the grace of communion."
Secondly, because he does penance negligently, wherefore it is written in the same Distinction (OBJ 3): "We can be sure that those who show no signs of humble compunction, or of earnest prayer, who avoid fasting or study, would exercise their former duties with great negligence if they were restored to them."
Thirdly, if he has committed a sin to which an irregularity is attached; wherefore it is said in the same Distinction (Objection [3]), quoting the council of Pope Martin [*Martin, bishop of Braga]: "If a man marry a widow or the relict of another, he must not be admitted to the ranks of the clergy: and if he has succeeded in creeping in, he must be turned out. In like manner, if anyone after Baptism be guilty of homicide, whether by deed, or by command, or by counsel, or in self-defense." But this is in consequence not of sin, but of irregularity.
Fourthly, on account of scandal, wherefore it is said in the same Distinction (Objection [3]): "Those who have been publicly convicted or caught in the act of perjury, robbery, fornication, and of such like crimes, according to the prescription of the sacred canons must be deprived of the exercise of their respective orders, because it is a scandal to God's people that such persons should be placed over them. But those who commit such sins occultly and confess them secretly to a priest, may be retained in the exercise of their respective orders, with the assurance of God's merciful forgiveness, provided they be careful to expiate their sins by fasts and alms, vigils and holy deeds." The same is expressed (Extra, De Qual. Ordinand.): "If the aforesaid crimes are not proved by a judicial process, or in some other way made notorious, those who are guilty of them must not be hindered, after they have done penance, from exercising the orders they have received, or from receiving further orders, except in cases of homicide."