When I had now finished the books of Spiritual Conferences, the merit of which consists in the thoughts expressed rather than in the language used (since my rude utterances were unequal to the deep thoughts of the saints), I had contemplated and almost determined on taking refuge in silence (as I was ashamed of having exposed my ignorance) that I might as far as possible make up for my audacity in speaking by modestly holding my tongue for the future. But you have overcome my determination and purpose by your commendable earnestness and most urgent affection, my dear Leo, my esteemed and highly regarded friend, ornament that you are of the Roman Church and sacred ministry, 2361 as you drag me forth from the obscurity of the silence on which I had determined, into a public court which I may well dread, and oblige me to undertake new labours while I am still blushing for my past ones. And though I was unequal to lesser tasks, you compel me to match myself with greater ones. For even in those trifling works, in which of our small ability we offered some small offering to the Lord, I would never have attempted to do or apply myself to anything unless I had been led to it by Episcopal command. And so through you there has been an increase of importance both of our subject and of our language. For whereas before we spoke, when bidden, of the business of the Lord, you now require us to speak of the actual Incarnation and glory of the Lord Himself. And so we who were formerly brought as it were into the holy place of the temple by priestly hands, now penetrate under your guidance and protection, so to speak, into the holy of holies. Great is the honour but most perilous the undertaking, 2362 because the prize of the holy sanctuary and the divine reward can only be secured by a victory over our foe. And so you require and charge us to raise our feeble hands against a fresh heresy and a new enemy of the faith, 2363 and that we should take our stand, so to speak, against the awful open-mouthed gapings of the deadly serpent, that at my summons the power of prophecy and the divine force of the gospel word may destroy the dragon now rising up with sinuous course against the Churches of God. I obey your intreaty: I yield to your command: for I had rather trust in my own matters to you than to myself, especially as the love of Jesus Christ my Lord commands me this as well as you, for He Himself gives me this charge in your person. For in this matter you are more concerned than I am, as your judgment stands in peril rather than my duty. For in my case, whether I prove equal to what you have commanded me or no, the very fact of my obedience and humility will be in some degree an excuse for me; if indeed I might not urge that there is more value in my obedience, if there is less that I can do. For we easily comply with any ones orders, out of our abundance: but his is a great and wonderful work, whose desires exceed his powers. Yours then is this work and business, and yours it is to be ashamed of it. Pray and intreat that your choice may not be discredited by my clumsiness; and that, supposing we do not answer the expectations which you have formed of us, you may not seem to have been wrong in commanding out of an ill-considered determination, while I was right in yielding, owing to the claims of obedience.
Mi Leo, veneranda ac suscipienda caritas mea, Romanæ ecclesiæ ac divini ministerii decus (Petschenig). Gennadius (De Vir. Illust. c. lxi.) tells us of Cassian, that “finally at the request of Leo, then archdeacon of Rome and afterwards Bishop, he wrote seven books against Nestorius on the Incarnation of the Lord, and thus brought to a close his literary labours at Marseilles, as well as his life, in the reign of Theodosius and Valentinian. The date of the work must have been a.d. 430, shortly before the Council of Ephesus.549:2362 549:2363
Nestorius had been consecrated Bishop of Constantinople in a.d. 428, and very shortly afterwards joined Anastasius in the denial that God could be born of a woman, and developed the heresy associated with his name.