St. Isaac is fully accepted as a saint in the Orthodox Church, though during his lifetime, he was [[canons (law)|canonically]] a member of the [[Assyrian Church of the East|Church of the East]], a church that has been associated with the [[Nestorianism|Nestorian heresy]], although that charge is contested today. His writings nevertheless came to be extremely popular in Orthodox monastic circles and are well-known for their Orthodoxy. Most contemporary Nestorians rejected St. Isaac's three theses, which, although they are not known in their exact form, were Orthodox and incompatible with the Nestorian heresy.[http://www.newadvent.org/cathen/08176a.htm] One of his extant prayers to Christ makes it difficult for one to maintain that the holy monk was a Nestorian.[http://www.newadvent.org/cathen/08176a.htm] [[Veneration]] for him grew, and he came to be incorporated into the Orthodox calendar of saints.