Nicene and Post-Nicene Fathers, Ser. II, Vol. XI:
The Works of John Cassian.: Chapter XXXVI. The answer, telling that this question should be reserved for a future Conference.

Chapter XXXVI.

The answer, telling that this question should be reserved for a future Conference.

Theonas: Your zeal indeed, whereby you desire to reach the way of perfection, not for a moment only but fully and perfectly, urges us to continue this discussion unweariedly. For you are anxiously inquiring not about external chastity or outward circumcision, but about that which is secret, as you know that complete perfection does not consist in this visible continence of the flesh which can be attained either by constraint, or by hypocrisy even by unbelievers, but in that voluntary and invisible purity of heart, which the blessed Apostle describes as follows: “For he is not a Jew which is so outwardly, nor is that circumcision which is outward in the flesh, but he is a Jew which is one inwardly, and the circumcision is that of the heart, in the spirit not in the letter, whose praise is not of men but of God,” 2228 who alone searches the secrets of the heart. But because it is not possible for your wish to be fully satisfied (as the short space of the night that is left is not enough for the investigation of this most difficult question,) I think it well to postpone it for a while. For these matters, as they should be propounded by us quietly and with an heart entirely free from all bustling thoughts, so should they be received into your minds; for just as the inquiry ought to be undertaken for the sake of our common purity, so they cannot be learnt or acquired by one who is without the gift of uprightness. For we do not ask what arguments of empty words, but what the inward faith of the conscience and the greater force of truth can persuade. And therefore with regard to the knowledge and teaching of this purification nothing can be brought forward except by one who has had experience of it, nor can anything be committed except to one who is a most eager and very earnest lover of the truth itself, who does not hope to attain it by asking questions with mere vain words, but by striving with all his might and main, with no wish for useless chattering but with the desire to purify himself internally.

Footnotes

Rom. 2:28, 29.