Parallel to his Harvard thesis, John Zizioulas undertook the preparation of a theological thesis for the University of Athens, on the subject of Ecclesiology based on the sources of the first centuries. This doctoral study finally received the title: “The Unity of the Church in the Holy Eucharist and the Bishop”, and was submitted to the Theological School of the University of Athens, by which it was finally accepted in 1966 with extremely laudatory comments from all the judging professors and with an unanimous award of the “excellent” grade.

The fact that it is not possible in Greece to teach in an Orthodox Theological School, if the doctoral thesis and the doctoral diploma have not been approved by an Orthodox Theological School, obliged him to give priority and finally limit himself to obtaining a doctoral diploma of his Orthodox Theological School University of Athens with the perspective of his academic career in Greece.