9 But it is scarcely possible to express how great is the utility of the light of doctrine which shines from the clergy, and is poured among the different orders of Christian people, if indeed it shines as it were from a beacon of virtue. For in the precepts which tend to the correction of men's morals, the acts of their masters are of more avail than their precepts, nor will any easily feel confidence when dealing with one whose deeds do not accord with his words and precepts. We turn Our eyes and minds to Jesus Christ; who, as He is the truth , has taught Us what We ought to believe, as He is the life and way , has offered Himself to Us a perfect example, how We should lead a good life and eagerly seek after Our final good. He Himself desired His disciples to be ordered and perfected after His own pattern, "so let your light shine," that is in doctrine "before men, that they may see your good works," not differing from the principles of your doctrine "and glorify your Father Who is in heaven" ( Mat . v. 16.), having combined together the doctrine and excellence of the gospel which He committed to them to preach. It is right that those precepts should be divine by which the life of priests is ordered and directed. Above all it is necessary that they persuade themselves and have it almost written in their minds, that they are now no longer in. the companionship of God, and though passing their time in the communion of the world, still live the life of Christ our Lord. Who if they really live by Him and in Him, will in no way seek "those things which are their own," but will be entirely taken up with "those things which belong to Jesus Christ" ( Philipp . ii. 21), nor will they receive the empty favour of men, but will seek after the solid favour of God; they will, moreover, abstain from and abhor these lower and contemptible things, and industriously trying to become rich in heavenly blessings, will generously and gladly pour them forth, as is the part of holy charity; further, they will never permit themselves to oppose or prefer their own to the judgement and will of the bishops, but by obeying and giving way to them as bearing the person of Christ, they will obtain most happily in the Lord's vineyard abundance of most choice fruit which will remain with them forever. But whosoever severs himself in thought or will from his shepherd and from the chief of shepherds, the Roman Pontiff, is in no way joined to Christ, "he that heareth you heareth Me, and he that despiseth you despiseth Me" ( Luke x. 16), but whosoever is separated from Christ scatters rather than gathers together-whence, moreover, is evident the kind and measure of consideration due to men who are placed in positions of public authority. For it is by no means intended that any one should desire to deny or derogate from their rights; rather those are to be diligently observed by other citizens, and especially carefully by priests: "Render to Caesar the things which are Caesar's." ( Matt . xxii. 21.) For those functions are most noble and honourable which God the highest lord and ruler has imposed upon men who are princes, that, by counsel, reason, and all care of justice they should govern, preserve, and increase the state. Wherefore let the clergy carefully attend to and perform every duty as citizens, not after the manner of one who is servile, but of one who holds them in reverence, on account of religion, not on account of fear; at the same time with due observance, maintaining their own dignity, being both citizens and priests of God. But if it should happen that the civil power should invade the rights of God and of His Church, then let a marked example be set by priests, as every Christian man ought to persevere in the path of duty during times of religious trouble; let him bear many things in silence, with unstained virtue; let him be cautious in bearing evil deeds, nor let him ever assent or consent to the wicked in any matter; but if it be a question of choice which he should do, whether the laws of God were to be broken or men pleased let him freely use that memorable and most dignified answer of the Apostles: "We ought to obey God rather than men." ( Acts v. 29.)
Source: Officio Sanctissimo (Vatican.va)