 According to the most probable tradition he was enabled through the influence he had with King Yazdgerd I, to restore the Catholicate (patriarchate) of Seleucia, which had been vacant for twenty-two years.Another account says he was chosen to replace a certain Qayom, who had been deposed by his fellow-bishops for incapacity.Isaac's great work was the organizing of the Council of Seleucia, the equivalent for the Eastern Syrian Church of the First Council of Nicaea.