Why do you think priests were so influential in ancient sumerian society?

In the ancient Sumerian society, the priests were so influential because people thought that they were the representatives of God. People beleived in God but they could not see them. The priests took advantage of the fear of god among people to become very influential in the Sumerian society. The common people were of the opinion that the Gods used to speak to them through the help of these priests. The priests were so powerful during those times that they even became rulers of certain city-states. Actually they were taking advantage of the beliefs of the common people.