It might sound odd to you, but all priests of that age were also scientists. Conversely, the scientists who possessed high spiritual power became the priests.
Their scientific researches were directly connected to the development of the spiritual power. Being superior in spiritual power and closer to God, and they were considered to be more excellent. This can be regarded as a kind of a theocracy in the sense that the ones who were close to God governed the kingdom.
Scientists at that era didn't move toward materialism like the current civilization. Of course, it had been generally understood that the real entity of the human is a spirit and there is a reincarnation. People possessed a considerably high spiritual power of perception.
For them, God was the existence like a source of spiritual power. The most important theme for them was how they could draw the spiritual power from God. The recognition that "God is the energy of love" had already forgotten long ago.
The appointment of the priest was done very strictly by using ability tests in the beginning. However, it moved gradually to a hereditary system. Even if one did not have any excellent recognition or spiritual power, one became a priest only by being born to the family of the priest.
The priests of that time owned many rights and interests, as well as a political power. To become a member of the council constituted of the priests meant to become part of the top of the ruling classes.
Channeling message by Amarie “Project Eden ~The Origin of Earth~” (Kindle)