Objection 1. It would seem that a penitent, at the point of death, cannot be absolved by any priest. For absolution requires jurisdiction, as stated above (Article 5). Now a priest does not acquire jurisdiction over a man who repents at the point of death. Therefore he cannot absolve him.
Objection 2. Further, he that receives the sacrament of Baptism, when in danger of death, from another than his own priest, does not need to be baptized again by the latter. If, therefore, any priest can absolve, from any sin, a man who is in danger of death, the penitent, if he survive the danger, need not go to his own priest; which is false, since otherwise the priest would not "know the countenance of his cattle."
Objection 3. Further, when there is danger of death, Baptism can be conferred not only by a strange priest, but also by one who is not a priest. But one who is not a priest can never absolve in the tribunal of Penance. Therefore neither can a priest absolve a man who is not his subject, when he is in danger of death.
On the contrary, Spiritual necessity is greater than bodily necessity. But it is lawful in a case of extreme necessity, for a man to make use of another's property, even against the owner's will, in order to supply a bodily need. Therefore in danger of death, a man may be absolved by another than his own priest, in order to supply his spiritual need.
Further, the authorities quoted in the text prove the same (Sent. iv, D, 20, Cap. Non Habet).
I answer that, If we consider the power of the keys, every priest has power over all men equally and over all sins: and it is due to the fact that by the ordination of the Church, he has a limited jurisdiction or none at all, that he cannot absolve all men from all sins. But since "necessity knows no law" [Cap. Consilium, De observ. jejun.; De reg. jur. (v, Decretal)] in cases of necessity the ordination of the Church does not hinder him from being able to absolve, since he has the keys sacramentally: and the penitent will receive as much benefit from the absolution of this other priest as if he had been absolved by his own. Moreover a man can then be absolved by any priest not only from his sins, but also from excommunication, by whomsoever pronounced, because such absolution is also a matter of that jurisdiction which by the ordination of the Church is con. fined within certain limits.
Reply to Objection 1. One person may act on the jurisdiction of another according to the latter's will, since matters of jurisdiction can be deputed. Since, therefore, the Church recognizes absolution granted by any priest at the hour of death, from this very fact a priest has the use of jurisdiction though he lack the power of jurisdiction.
Reply to Objection 2. He needs to go to his own priest, not that he may be absolved again from the sins, from which he was absolved when in danger of death, but that his own priest may know that he is absolved. In like manner, he who has been absolved from excommunication needs to go to the judge, who in other circumstances could have absolved him, not in order to seek absolution, but in order to offer satisfaction.
Reply to Objection 3. Baptism derives its efficacy from the sanctification of the matter itself, so that a man receives the sacrament whosoever baptizes him: whereas the sacramental power of Penance consists in a sanctification pronounced by the minister, so that if a man confess to a layman, although he fulfills his own part of the sacramental confession, he does not receive sacramental absolution. Wherefore his confession avails him somewhat, as to the lessening of his punishment, owing to the merit derived from his confession and to his repentance. but he does not receive that diminution of his punishment which results from the power of the keys; and consequently he must confess again to a priest; and one who has confessed thus, is more punished hereafter than if he had confessed to a priest.
Source: Summa Theologica (New Advent)