In Egyptian temples, being a priestess or priest (I am using the term very broadly here for all temple personnel) meant serving in the temples. Such service might include performing the rites that were considered necessary to ensure the proper relationship between the Goddess, the kingship, the land and people of Egypt, and ultimately, the universe. It might include everything from cleaning the temple, arranging flowers, and playing music for the Goddess, to hearing the needs of the people outside the temple through the “priest holes” in the walls where oracles of the Goddess were sometimes given.
It also meant certain restrictions on personal life—especially while serving in the temple. Among these might be purity restrictions of a variety of kinds, including personal cleanliness, sexual abstinence, and abstinence from certain foods.
Oh, by the way…I am sorry to report that Egyptian priestesses normally had lesser roles in Egyptian temples than priests did. Yes, there were some powerful priestesses—the queen, for example, or the God’s Wife of Amun—but for the most part, women were in support roles rather than leadership roles and this became increasingly true as time went by. Some scholars believe that this change in women’s status in the temples reflected a change in society. But it also may have had to do with the increased “purity” restrictions that were enforced during later periods.
You see, because women had babies and menstruated monthly, they could not be “pure” for a long enough stretch of time, as long as three months. In other words—as has so often been the case historically—women were “defined out” because of their physical differences from men. A woman can’t be pure because she’s a woman! But I rant. Back to the topic at hand…
Purity restrictions were also important in the Greek and Roman Isis temples. In the Roman period, priestesses and priests of Isis were particularly known for their chastity. We have records of a number of women who were vowed to Isis as virgins for their lifetimes.
Strangely (to us) this virginity often increased women’s power—because it took them out of sexual roles. As time went on, Roman women gained power; and some Roman priestesses could even approach the High Altar and perform important ritual functions in the temples of Isis. In fact, some religious scholars have opined that the religion of Isis was more favorable to women than any other religion. Yet there were many, many male devotees and priests of Isis. Generally, men and women followed Isis in more or less equal numbers.
In addition to their chastity, the priests of Isis were renowned for was their breadth of knowledge. This was true specifically of Isiac priests in the later period when the religion spread throughout the Mediterranean. There is a literary example in which a priest of Isis is specifically referred to as a scholar. But this was true generally of Egyptian priests—and to some extent priestesses—of the Per Ankh, the House of Life. They all had a reputation for being well educated in subjects of all kinds, from spirituality to diplomacy. For example, those undergoing the famous Mysteries of Isis expected to receive knowledge about the Goddess from the priestesses and priests who helped conduct the Mystery experience.
Okay. So far we have two qualities we can associate with Isis’ priestesses and priests: service and knowledge. However, today we usually associate priest/esshood with a particular spiritual relationship with the Goddess. Is there any historical evidence for this type of relationship with Isis by her priestesses and priests? We’ll take a look at that next time.
Isiopolis 
Explain how and which women were chosen to be priestess of Isis.
In the large and important Egyptian temples, priestesshood was (sad, but true) a privilege of royal and noble families. I don’t really know how the priestesses might have been chosen out in the smaller towns and villages. When the worship of Isis came to Greece and Rome, one gets the impression that there it was more of a vocational choice, but you would have had to have been able to make that choice for yourself—and that usually means having some money and/or position. (We know that votaries of the Goddess might be called in dream in Greece and Rome—and this must have been true in Egypt as well.) Apart from having the beautiful facilities and support structure of the temples, I think we are more fortunate today in that modern priestess and priests of Isis make their own choice to love Her—and, of course, the Goddess Herself often chooses them.