
Leontios, Archbishop of Caesarea, had consecrated St. Gregory, and the Byzantines believed that this made him and those that he converted beholden to the diocese of the Archbishop of Caesarea.
The Armenians argued that although St. Gregory had converted their king, the tradition of Armenian Christianity was actually much older, having been started by the conversions of the Apostles Thaddeus and Bartholomew back in the few decades after the death of Christ.
This apostolic origin, in their eyes, gave them an inviolable right to an autonomous church, since their church had in fact been created around the same time that the first Christian missionaries ventured outside of Palestine.

Image: St. Gregory