Each virtue lies between the unnatural passions. Moral judgment lies between craftiness and thoughtlessness; self-restraint, between obduracy and licentiousness; courage, between overbearingness and cowardice; justice between over-frugality and greed. The four virtues constitute an image of the heavenly man, while the eight unnatural passions constitute an image of the earthly man (see I Corinthians 15:49).God possesses a perfect knowledge of all these things, just as He knows the past, the present and the future; and they are known to some extent by him who through grace has learned from God about His works, and who through this grace has been enabled to realize in himself that which is according to God’s image and likeness (see Genesis 1:26). But if someone claims that, simply by hearing about these things, he knows them as he should, he is a liar. Man’s intellect can never rise to heaven without God as a guide; and it cannot speak of what it has not seen, but must first ascend and see it. On the level of hearsay, you should speak only of things that you have learned from the Scriptures, and then with circumspection, confessing your faith in the Father of the Logos, as St. Basil the Great puts it, and not imagining that through hearsay you possess spiritual knowledge; for that is to be worse than ignorant.
As St. Maximos has said, “To think that one knows prevents one from advancing in knowledge.” St. John Chrysostom points out that there is an ignorance which is praiseworthy: it consists in knowing consciously that one knows nothing. In addition, there is a form of ignorance that is worse than any other: not to know that one does not know. Similarly, there is a knowledge that is falsely so called, which occurs when, as St. Paul says, one thinks that one knows but does not know (see I Corinthians 8:2).
from G. E. H. Palmer, Philip Sherrard, and Bishop Kallistos Ware, “The Philokalia: vol. III,” (London: Faber and Faber, 1984), pp. 100 – 101