2 But it is neither the part of an emperor to refuse liberty of speech, nor of a priest not to say what he thinks. For there is nothing in you emperors so popular and so estimable as to appreciate freedom in those even who are in subjection to you by military obedience. For this is the difference between good and bad princes, that the good love liberty, the bad slavery. And there is nothing in a priest so full of peril as regards God, or so base in the opinion of men, as not freely to declare what he thinks. For it is written: “I spoke of Your testimonies before kings, and was not ashamed;” and in another place: “Son of man, I have set You a watchman unto the house of Israel, in order,” it is said, “that if the righteous does turn from his righteousness, and commit iniquity, because you have not given him warning,” that is, hast not told him what to guard against, “the memory of his righteousness shall not be retained, and I will require his blood at your hand. But if you warn the righteous that he sin not, and he does not sin, the righteous shall surely live because you have warned him, and you shall deliver your soul.”
Source: Letters (New Advent)