In this world there are many different kinds of knowledge; their variety is as great as that of the Arts and Sciences. But while all of them are either completely useless, or are of advantage only with regard to the needs of this present life, yet there in none of them which does not have its own peculiar method and system of learning it, whereby it may be attained by those wishing to acquire it….how much more does the study and practice of our religion demand a proper order and plan, the religion that leads us to the contemplation of hidden and invisible mysteries, and aims not at present gain, but at eternal rewards.
The knowledge thereof is twofold; first the practical, which consists in amendment of living and extirpation of vices; and second, the theoretical, which is occupied with contemplation of divine truths, and the perception of all that is most sacred….the practical can indeed be possessed without the theoretical but without the practical the theoretical can never be grasped at all.
…he who does not free himself from the condition of sin strives in vain to reach the vision of God. “For the Holy Spirit of discipline will flee from the deceitful, and will withdraw Himself from thoughts that are without understanding, and He shall not abide where iniquity cometh in” (Wisdom of Solomon 1:4-5).
~St John Cassian (Conference with Abbot Nesteros)