De Ebrietate

And ignorance does produce completely similar effects on the soul, depriving it of its faculties of seeing and of hearing, and allowing neither light nor reason to enter into it, lest the one should instruct it and the other should exhibit the truth to it. But shedding upon it dense darkness and abundant folly, it renders the most beautiful soul a deaf, and dumb, and lifeless stone.

For knowledge, which is the opposite of ignorance, may be called, in a manner, the eyes and ears of the soul; for it applies the mind to what is said, and fixes its eyes upon things as they exist, and cannot endure to form a false judgment of anything which it either sees or hears. But it examines and carefully surveys every object which is worthy of being seen or heard, and even if it be necessary to sail or to travel over sea and land, it will traverse them to its furthest boundaries that it may see anything more important, or hear anything more modern;

for the love of knowledge admits of no hesitation or delay, it is an enemy to sleep and a friend to waking. Therefore, continually rousing up, and awakening, and sharpening the intellect, it compels it to roam about in every direction, where instruction is to be obtained, inspiring it with an avidity for hearing, and infusing into it an insatiable thirst for learning.

Therefore knowledge causes hearing and seeing, by means of which faculties success and rectitude of conduct are arrived at; for he who sees and hears, knowing what is expedient, chooses that, and rejecting the contrary is benefited by his knowledge. But ignorance causes to the soul a mutilation more grievous than the mutilation of the body, and is the cause of many errors, since it is unable to derive any assistance from without, either by foreseeing anything, or by any acuteness of hearing. Therefore, owing to its exceeding desolateness of condition, it is left utterly undefended and unprotected, and is exposed to the plots of all kinds of men and to dangers from all kinds of events.