26 The experience of twenty centuries fully and gloriously reveals the power for good of the word of the priest. Being the faithful echo and reecho of the "word of God," which "is living and effectual and more piercing than any two-edged sword,' it too reaches "unto the division of the soul and spirit"; it awakens heroism of every kind, in every class and place, and inspires the self forgetting deeds of the most generous hearts. All the good that Christian civilization has brought into the world is due, at least radically, to the word and works of the Catholic priesthood. Such a past might, to itself, serve as sufficient guarantee for the future; but we have a still more secure guarantee, "a more firm prophetical word" in the infallible promises of Christ.
Source: Ad Catholici Sacerdotii (Vatican.va)