34 For this reason even in the Old Testament God commanded His priests and levites: "Let them therefore be holy because I am also holy: the Lord who sanctify them." In his canticle for the dedication of the temple, Solomon the Wise made this same request to the Lord in favor of the sons of Aaron: "Let Thy priests be clothed with justice: and let Thy saints rejoice." So, Venerable Brethren, may we not ask with St. Robert Bellarmine: "If so great uprightness, holiness and lively devotion was required of priests who offered sheep and oxen, and praised God for the moral blessings; what, I ask, is required of those priests who sacrifice the Divine Lamb and give thanks for eternal blessings?" "A great dignity," exclaims St. Lawrence Justinian, "but great too is the responsibility; placed high in the eyes of men they must also be lifted up to the peak of virtue before the eye of Him who seeth all; otherwise their elevation will be not to their merit but to their damnation."
Source: Ad Catholici Sacerdotii (Vatican.va)