The article provides a historical analysis of adoption and spread of Christianity (the Christianization) as a state religion in Armenia during the reign of the Armenian king Tiridates III the Great (A. D. 287–330) and in the days of St. Gregory the Illuminator (Grigory Partev), the first enlightener and spiritual mentor of the Catholicos of the Armenian Apostolic Church, as well as relation of the religion to military service, the role of the church and the actions of clergymen in different periods of history in the army of Armenia. The article discloses formation of military spiritual service, forms and methods of activities of regimental chaplains both in peacetime and in wartime, aimed at carrying out activities that contribute to the formation of persistent moral-combat and moral-spiritual qualities among military personnel. Examples from the Holy Book in relation to military service are given.