The subject of the study is various terms denoting "service," each of which in different periods of time and in different religious environments becomes the main term denoting sacred service. The dissertation explores the causes of these terminological changes and the evolution of the concept of "sacred service," which is behind the change of terms. The concept of "service" brings us to the diaconate in the early church, which became a kind of institution of "service to one's neighbor." The dissertation explores the history of the emergence, development and official duties of the diaconate and two related institutions - deaconesses and subdeacons.