The Great Union celebrated on 1 December 1918 represents the collective effort of the entire Romanian people, an effort which, corroborated with the support and acceptance of the Great Powers, crowned a millenary wish of the Romanians, the union of all in one national state. Promoting the ideas of national unity, the civic spirit, and especially the desire of patriotism, an important support for the Romanian state was given by the Romanian Orthodox Church, which through priests, monks and hierarchs not only preached the sacrifice, but gave the example of sacrifice by the priests and the mourners of the nation. The religious factor was exploited by war propaganda, having deep roots since the War of Independence. Encouraging the population to serve the noble cause of the liberation of Transylvania, had both patriotic and religious support, as well as economic - the promise of appropriating those who will fight. The present paper seeks to highlight in a systematic, objective and chronological manner the main moments of the active involvement of the clergy in support of the Romanian army and in the life of the Romanian society in the context of the Great Union.