The normative Christology of the Assyrian church was written by Babai the Great ( 551 -- 628 ) and is clearly different from the accusations of dualism directed toward Nestorius : his main christological work is called the ` Book of the Union ' , and in it Babai teaches that the two qnome ( essences ) are unmingled but everlastingly united in the one parsopa ( personality ) of Christ . The normative Christology of the Assyrian church was written by Babai the Great ( 551 â `` 628 ) during the controversy that followed the First Council of Ephesus ( 451 ) . Babai held that within Christ there exist two qnome ( essences , or hypostases ) , unmingled , but everlastingly united in the one parsopa ( personality ) .