I have a question. I think that I have heard him called in Armenian "Soorp Sahag Asoree." That literally means "St. Isaac the Assyrian." Yet in English he is "St. Isaac the Syrian." Fifteen hundred years ago, would there not have been an ethnic distinction between Assyrians and Syrians?
I think calling him Syrian was simply a way for the EO and OO to undermine his affiliation with the Church of the East. For the same reason, according to the Catholic Encyclopedia
, "the monophysites falsified his biography, placing his life at the beginning of the seventh century, making him a monk of the Jacobite monastery of Mar Mattai, and stating that he retired to the desert of Scete in Egypt."