It is probable, however, that to such remarks as the above, the answer returned would be, that he was pious who kept the laws of his own country, and not at all chargeable with impiety for the non-observance of those of other lands; and that, again, he who was deemed guilty of impiety among certain nations was not really so, when he worshipped his own gods, agreeably to his country's laws, although he made war against, and even feasted on, those who were regarded as divinities among those nations which possessed laws of an opposite kind.
Now, observe here whether these statements do not exhibit the greatest confusion of mind regarding the nature of what is just, and holy, and religious; since there is no accurate definition laid down of these things, nor are they described as having a peculiar character of their own, and stamping as religious those who act according to their injunctions. If, then, religion, and piety, and righteousness belong to those things which are so only by comparison, so that the same act may be both pious and impious, according to different relations and different laws, see whether it will not follow that temperance also is a thing of comparison, and courage as well, and prudence, and the other virtues, than which nothing could be more absurd!
What we have said, however, is sufficient for the more general and simple class of answers to the allegations of Celsus. But as we think it likely that some of those who are accustomed to deeper investigation will fall in with this treatise, let us venture to lay down some considerations of a profounder kind, conveying a mystical and secret view respecting the original distribution of the various quarters of the earth among different superintending spirits; and let us prove to the best of our ability, that our doctrine is free from the absurd consequences enumerated above.
Source: Against Celsus (New Advent)