The Conferences Of John Cassian by John Cassian
Chapter XVI. That the rational part of our soul is corrupt.
And therefore if you want to discover the source and origin of this fault, you must recognize that the rational part of your mind and soul is corrupt, that part namely from which the faults of presumption and vainglory for the most part spring. Further this first member, so to speak, of your soul must be healed by the judgment of a right discretion and the virtue of humility, as when it is injured, while you fancy that you can not only still scale the heights of perfection but actually teach others, and hold that you are capable and sufficient to instruct others, through the pride of vainglory you are carried away by these vain rovings, which your confession discloses. And these you will then be able to get rid of without difficulty, if you are established as I said in the humility of true discretion and learn with sorrow of heart how hard and difficult a thing it is for each of us to save his soul, and admit with the inmost feelings of your heart that you are not only far removed from that pride of teaching, but that you are actually still in need of the help of a teacher.