If it is the fact that men bearing the name of Romans are found to be enemies of Rome, why are we, on the ground that we are regarded as enemies, denied the name of Romans? We may be at once Romans and foes of Rome, when men passing for Romans are discovered to be enemies of their country. So the affection, and fealty, and reverence, due to the emperors do not consist in such tokens of homage as these, which even hostility may be zealous in performing, chiefly as a cloak to its purposes; but in those ways which Deity as certainly enjoins on us, as they are held to be necessary in the case of all men as well as emperors.
Deeds of true heart-goodness are not due by us to emperors alone. We never do good with respect of persons; for in our own interest we conduct ourselves as those who take no payment either of praise or premium from man, but from God, who both requires and remunerates an impartial benevolence. We are the same to emperors as to our ordinary neighbors. For we are equally forbidden to wish ill, to do ill, to speak ill, to think ill of all men. The thing we must not do to an emperor, we must not do to any one else: what we would not do to anybody, a fortiori, perhaps we should not do to him whom God has been pleased so highly to exalt.
Source: The Apology (New Advent)