How can we assist the souls suffering in purgatory? 1. By our prayers. The Holy Scripture says; It is a holy and a wholesome thought to pray for the dead, that they may be loosed from sins. The Catholic Church has therefore always taught that the prayer of the faithful for the departed is holy and wholesome. 2. By the holy sacrifice of the Mass, the fruits of which are most beneficial to the souls in purgatory. For this reason holy Church has always, from the time of the apostles, remembered the dead in the holy Mass. 3. By gaining indulgences, and other good works, by which we supplicate God to show mercy to the souls of the suffering, to accept what is performed by us in satisfaction for the punishment to be endured by them, and to bring them into the kingdom of everlasting peace and light. (Goffine’s Devout Instructions, 1896)
If anyone says that after the reception of the grace of justification the guilt is so remitted and the debt of eternal punishment so blotted out to every repentant sinner that no debt of temporal punishment remains to be discharged, either in this world or in Purgatory, before the gates of Heaven can be opened, let him be anathema.
Since the Catholic Church, instructed by the Holy Ghost, has, following the sacred writings and the ancient tradition of the Fathers, taught in sacred councils and very recently in this ecumenical council, that there is a Purgatory, and that the souls there detained are aided by the suffrages of the faithful and chiefly by the Acceptable Sacrifice of the Altar, the Holy Council commands the bishops that they strive diligently to the end that the sound doctrine of Purgatory, transmitted by the Fathers and sacred councils, be believed and maintained by the faithful of Christ, and be everywhere taught and preached.
Canons Concerning The Sacrament Of Penance. The Council of Trent. Session XIV, November 25, 1551
CANON 12. If anyone says that God always pardons the whole penalty together with the guilt and that the satisfaction of penitents is nothing else than the faith by which they perceive that Christ has satisfied for them, let him be anathema.
CANON 13. If anyone says that satisfaction for sins, as to their temporal punishment, is in no way made to God through the merits of Christ by the punishments inflicted by Him and patiently borne, or by those imposed by the priest, or even those voluntarily undertaken, as by fasts, prayers, almsgiving or other works of piety, and that therefore the best penance is merely a new life, let him be anathema.
CANON 14. If anyone says that the satisfactions by which penitents atone for their sins through Christ are not a worship of God but traditions of men, which obscure the doctrine of grace and the true worship of God and the beneficence itself of the death of Christ, let him be anathema.
CANON 15. If anyone says that the keys have been given to the Church only to loose and not also to bind, and that therefore priests, when imposing penalties on those who confess, act contrary to the purpose of the keys and to the institution of Christ, and that it is a fiction that there remains often a temporal punishment to be discharged after the eternal punishment has by virtue of the keys been removed, let him be anathema.
Chapter IX— On the Works Of Satisfaction. Session XIV. The Council of Trent. November 25, 1551.
It [the Council] teaches furthermore that the liberality of the divine munificence is so great that we are able through Jesus Christ to make satisfaction to God the Father, not only by punishments voluntarily undertaken by ourselves to atone for sins, or by those imposed by the judgment of the priest according to the measure of our offense, but also, and this is the greatest proof of love, by the temporal afflictions imposed by God and borne patiently by us.