Why Read "Old" Books?

Reading old books is often hard work. Mark Twain once quipped that a classic book is one "everyone wishes they have read but never takes the time to read." So, here is some encouragement from CS Lewis for us to prioritize reading "classics."

CS Lewis writes,

None of us can fully escape this [cultural] blindness [of our age], but we shall certainly increase it, and weaken our guard against it, if we read only modern books. Where they are true they will give us truths which we half knew already. Where they are false they will aggravate the error with which we are already dangerously ill. The only palliative is to keep the clean sea breeze of the centuries blowing through our minds, and this can be done only by reading old books. Not, of course, that there is any magic about the past. People were no cleverer then than they are now; they made as many mistakes as we. But not the same mistakes. They will not flatter us in the errors we are already committing; and their own errors, being now open and palpable, will not endanger us. . . . To be sure, the books of the future would be just as good a corrective as the books of the past, but unfortunately we cannot get at them. 

("On the Reading Old Books," in God in the Dock, pg. 202. I found this quote in The Devoted Life: An Invitation to the Purtian Classics, ed. by Kapic and Gleason, pg. 34.).