Isaac saw the clergy of the ancient world as something to aspire to. To him, they were the "entire intelligentsia"¹ of the ancient world, and he very much hoped that ADF would produce scholar-priests² who were specialists in sacrifice and all things ritual.
There is still a strong movement within ADF to continue this train of thought, aiming for the exclusion of some other types of priest (particularly the counselor-priest that is what most people think of when they see the word "priest"). Many of us are learning to accept that, while the "ritual specialist" is what we want our clergy to primarily be, we aren't having much luck escaping the role of counselor when things go wrong in our local Groves.
Generally, I see the function of an ADF Priest as two-fold: 1) to maintain the sacrifices, ensure that rituals are done at the right time and in the right way, and provide ritual help for those who aren't sure that what they're doing is "right" and those who are still learning the Old Ways as they advance through their own spiritual development; and 2) to be there when the folk need us, whether that be someone to speak to when their father dies, or someone to discuss their plans to purchase a new home through the medium of divination. The first function will always be primary in my eyes, though.
¹ - "IndoEuropean Paleopaganism and Its Clergy" - Isaac Bonewits, Druids' Progress # 1, 1984
² - "The Vision of ADF" - Isaac Bonewits