Stobaeus on Stoic Ethics 14

The Stoics say that only the wise man is a good prophet and poet and public speaker and dialectician and critic, but not every wise man, since some of these crafts also require a mastery of certain theorems. 

And prophecy is a theoretical knowledge of signs, significant for human life, given by the gods or daimons. The forms of prophecy are similarly described. 

They say that only the wise man is a priest but that no base man is. 

For the  priest must be experienced in the laws concerning sacrifices and prayers and purifications and foundations and all such things, and in addition he also needs ritual sanctity and piety and experience of service to the gods, and needs to be intimate with the nature of divinity. 

And the base man has not one of these features, and that is why all imprudent men are impious. 

For impiety, being a vice, is ignorance of the service to the gods, whereas piety is, as we said, a knowledge of service to the gods. 

Similarly they say that the base are not holy either; for holiness is defined in outline as justice toward the gods, whereas the base deviate in many respects from just action toward the gods, which is why they are unholy and impure and unsanctified and defiled, and to be barred from festivals. 

For they say that participating at a festival is a prerogative of the virtuous man, a festival being a time in which one should be concerned with the divine for the sake of honoring the gods and for the sake of the appropriate observations; and that is why the participant in a festival should accommodate himself to this sort of role with piety.