The Archimandrite Elias Mastrogiannopoulos (1919-2020) was an important figure of the Greek Orthodox church in the 20th century. He was one of the first theologians and ecclesiastical men to promote patristic studies after 1960, theological dialogue with non-Orthodox based on the ancient Christian tradition, as well as the re-evangelization of the Orthodox Christian Greeks through Sunday schools, confession and the frequent communion. Through his work, he advocated the active participation of the faithful in divine worship by participating in the election of bishops, the control of their faith and the teaching of the gospel. Although he does not hesitate to use non-Orthodox authors to support his arguments, he relies on his method mainly on the Bible and patristic tradition.