What is wrong with Mar Mattai, Michal?
Mar Mattai is, as far as I can tell, one of those "Pan-Syrian" kinds of saints who is beloved like Mar Isaac or Mar Ephrem, by everyone of that heritage. To probably belabor the point, I first read his story in a book by a Chaldean Catholic
author, but the monastery that bears his name is one of the oldest Syriac Orthodox
monasteries in Iraq, and maybe the world (founded 363 AD). The story of Mar Mattai is this: He fled the city of Amid (where he was born) during the persecutions of Julian the Apostate. He ended up in the mountains of Nineveh where he met Prince Behnam, who was the son of an Assyrian pagan king. During their time together Mar Mattai preached to Prince Behnam and also cured his sister Sarah of disease. Through his preaching, both were baptized, along with Behnam's companions. When their father (the pagan king) learned that they had accepted Christianity, he was enraged and killed his son and daughter. Later, he realized that he had made a mistake and in his grief over his loss and repentance for his sin, he had a monastery built bearing their names on the spot where Mar Mattai had healed Sarah. This monastery, like Mar Mattai monastery, still exists today, although according to Wikipedia
it has been administered by the Syriac Catholics of the village of Bakhdida since they converted to Rome starting in the 18th century (before that it had been Syriac Orthodox, and before that it had been Nestorian).
I love Mar Mattai because his story shows how simple preaching can bring even a murderer of his own children to the light, and I find the connection between these two monasteries very interesting for what it says about the richness of Syriac Christianity in Mesopotamia/Iraq (that they would pass through so many hands, and be equally beloved by all).
I do not believe that it is wrong to venerate Mar Mattai, even if he may have done his work among the Nestorians. He is recognized as a saint by our brothers and sisters in the Syriac Orthodox Church, and this is good enough for me. Plus, what an awesome story!