J. H. Kurtz, Church History, Volume 1 (of 3…
“ The age of Cyril of Alexandria marks an important turning point in the development of worship. It was natural that Cyril’s prevailing doctrine of the intimate connection of the divine and human natures in the person of Christ should have embodied itself in the services of the church. But this doctrine was yet at least one-sided theory which did not wholly exclude its perversion into error. In the dogma, indeed, thanks to the exertions of Leo and Theodoret, the still extant Monophysite error had no place given it. ”
