The order of our promise and course demands that there should follow the instruction of Abbot Nesteros, a man of excellence in all points and of the greatest knowledge: who when he had seen that we had committed some parts of Holy Scripture to memory and desired to understand them, addressed us in these words. There are indeed many different kinds of knowledge in this world, since there is as great a variety of them as there is of the arts and sciences. But, while all are either utterly useless or only useful for the good of this present life, there is yet none which has not its own system and method for learning it, by which it can be grasped by those who seek it. If then those arts are guided by certain special rules for their publication, how much more does the system and expression of our religion, which tends to the contemplation of the secrets of invisible mysteries, and seeks no present gain but the reward of an eternal recompense, depend on a fixed order and scheme. And the knowledge of this is twofold: first, πρακτική, i.e., practical, which is brought about by an improvement of morals and purification from faults: secondly, θεωρητική, which consists in the contemplation of things Divine and the knowledge of most sacred thoughts.
Reproduced in full. Translation: Nicene and Post-Nicene Fathers, series 2, vol. 11 (Schaff and Wace, 1894), public domain (Public domain).