Gregory took the opportunity to write another very long Oration as his apology for his flight.  In it he sets forth at great length his conception of the nature and responsibilities of the Priestly Office, and justifies himself both for having shrunk from such a charge, and for having so soon returned to take it up.  It is very improbable that this Oration, numbered II. in the Benedictine Edition, was ever delivered vivâ voce; but it was published, and is a complete Treatise on the Priesthood, used both by S. John Chrysostom as the foundation of his Six Books on the Priesthood, and by S. Gregory the Great as the basis of his Treatise on the Pastoral Rule.  It has also furnished material to many of the best Ecclesiastical writers of all ages.