Nicene and Post-Nicene Fathers: Series II/Volume XI/John Cassian/Conferences of John Cassian, Part II/Conference XIV/Chapter 15

Chapter XV.

An objection owing to the fact that many impure persons have knowledge while saints have not.

not seem to us founded on truth, or based on solid reasoning. For if it is clear that all who either never receive the faith of Christ at all or who corrupt it by the wicked sin of heresy, are of unclean hearts, how is it that many Jews and heretics, and Catholics also who are entangled
 * This assertion does

in various sins, have acquired perfect knowledge of the Scriptures and boast of the greatness of their spiritual learning, and on the other hand countless swarms of saintly men, whose heart has been purified from all stain of sin, are content with the piety of simple faith and know nothing of the mysteries of a deeper knowledge? How then will that opinion stand, which attributes spiritual knowledge solely to purity of heart?