22 These august powers are conferred upon the priest in a special Sacrament designed to this end: they are not merely passing or temporary in the priest, but are stable and perpetual, united as they are with the indelible character imprinted on his soul whereby he becomes "a priest forever"; whereby he becomes like unto Him in whose eternal priesthood he has been made a sharer. Even the most lamentable downfall, which, through human frailty, is possible to a priest, can never blot out from his soul the priestly character. But along with this character and these powers, the priest through the Sacrament of Orders receives new and special grace with special helps. Thereby, if only he will loyally further, by his free and personal cooperation, the divinely powerful action of the grace itself, he will be able worthily to fulfill all the duties, however arduous, of his lofty calling. He will not be overborne, but will be able to bear the tremendous responsibilities inherent to his priestly duty; responsibilities which have made fearful even the stoutest champions of the Christian priesthood, men like St. John Chrysostom, St. Ambose, St. Gregory the Great, St. Charles and many others.
Source: Ad Catholici Sacerdotii (Vatican.va)