From the first and lowest degree of knowledge, man moves on to the second, when he begins both in body and soul to practice the virtues: fasting, prayer, almsgiving, the reading of Holy Scripture, the struggle with the passions, and so forth.
Every good work, every goodly disposition of the soul in this second degree of knowledge, is begun and performed by the Holy Spirit through the working of this particular knowledge. The heart is shown the paths that lead to faith, even though this knowledge remains “bodily and composite.”
The third degree of knowledge is that of perfection. “When knowledge rises up above the earth and the care for earthly things and begins to examine its own interior and hidden thoughts, scorning that from which the evil of the passions springs and rising up to follow the way of faith in concern for the life to come … and in the seeking out of hidden mysteries—then faith takes this knowledge into itself and absorbs it, returning and giving birth to it from the beginning, so as to become itself ‘from the beginning,’ so as to become itself wholly spirit.”
Then it can “take wing and fly to the realm of incorporeal spirits and plumb the depths of the fathomless ocean, pondering on the divine and wondrous things that govern the nature of spiritual and physical beings and penetrating the spiritual mysteries that can only be grasped by a simple and supple mind.
Then the inner senses awaken to the work of the spirit in those things that belong to that other realm, immortal and incorruptible. This knowledge has, in a hidden way, here in this world, received already spiritual resurrection so as to bear true witness to the renewal of all things.”
These, according to St. Isaac, are the three degrees of knowledge with which the whole of man’s life is linked in body, soul and spirit. From the moment that he “begins to discern between good and evil to the moment of his leaving this world,” the soul’s knowledge is composed of one or all of these three degrees.
St Justin Popovich
