I think I mentioned before that priesthood in ancient Hellas was a lot different from priesthood as we understand it now. In the modern (Pagan) interpretation, priests serve a mostly spiritual role; they serve the religious community as a vessel for or to a God or Goddess. The primary tasks of a modern day priest(ess) seem to be to serve the community, to spread the gospel of the God(ess) in question and to offer access to the God(dess) in question.
During most festivals, an animal was sacrificed. It was the job of the priest(ess) to pick out the animal, lead it to the altar and bless the animal. Especially the latter was a job only a priest(ess) could perform, because they were especially well versed in liturgy, and because a failure to preform the exact rites would result in a failure of the sacrifice.