Moreover, we are to despise ingratiating ourselves with kings or any other men, not only if their favour is to be won by murders, licentiousness, or deeds of cruelty, but even if it involves impiety towards God, or any servile expressions of flattery and obsequiousness, which things are unworthy of brave and high-principled men, who aim at joining with their other virtues that highest of virtues, patience and fortitude. But while we do nothing which is contrary to the law and word of God, we are not so mad as to stir up against us the wrath of kings and princes, which will bring upon us sufferings and tortures, or even death.
For we read: “Let every soul be subject unto the higher powers. For there is no power but of God: the powers that be are ordained of God. Whosoever therefore resists the power, resists the ordinance of God.” These words we have in our exposition of the Epistle to the Romans, to the best of our ability, explained at length, and with various applications; but for the present we have taken them in their more obvious and generally received acceptation, to meet the saying of Celsus, that “it is not without the power of demons that kings have been raised to their regal dignity.”
Here much might be said on the constitution of kings and rulers, for the subject is a wide one, embracing such rulers as reign cruelly and tyrannically, and such as make the kingly office the means of indulging in luxury and sinful pleasures. We shall therefore, for the present, pass over the full consideration of this subject. We will, however, never swear by “the fortune of the king,” nor by ought else that is considered equivalent to God. For if the word “fortune” is nothing but an expression for the uncertain course of events, as some say, although they seem not to be agreed, we do not swear by that as God which has no existence, as though it did really exist and was able to do something, lest we should bind ourselves by an oath to things which have no existence.
If, on the other hand (as is thought by others, who say that to swear by the fortune of the king of the Romans is to swear by his demon), what is called the fortune of the king is in the power of demons, then in that case we must die sooner than swear by a wicked and treacherous demon, that ofttimes sins along with the man of whom it gains possession, and sins even more than he.
Source: Against Celsus (New Advent)