C. S. Lewis to an inquirer, as published in The Collected Letters of C. S. Lewis, 2:644:
I myself always index a good book when I read it for the first time noting (a) Linguistic phenomena. (b) Good & bad passages. (c) Customs: meal times, social classes, what they read etc. (d) Moral ideas. All this reading, though dedicated ad Dei gloriam [to the glory of God] in the long run must not be infected by any immediate theological, ethical, or philosophic reference. Your first job is simply the reception of all this work with your imagination & emotions. Each book is to be read for the purpose the author meant it to be read for: the story as a story, the joke as a joke.
This is a nice concise summary of principles more fully unpacked in Lewis’ book An Experiment in Criticism.
Tony Reinke 
Thanks for this. I love this quote. It gives me an idea of some things I’d like to index in my reading.
I put Lewis’ advice to the test not long ago when I read an obscure 15th century text, now hardly to be found, entitled, The Master of Fame. In this story a beleaguered and increasingly perplexed scribe working a troubled church and adjoining college reaches out to a theologian from another land in order to secure his help in correcting the theological drift of the joint institutions.The theologian, however, lives in a home and land that can be described as nothing short of paradise, while the clerk and his provincial and hidebound institution lies smack in the middle of a mosquito ridden swamp. What is more, his entry into the clerk’s sphere would mean nothing less than misunderstanding, persecution, and prolonged intellectual grief. To entice the theologian, the clerk offers a life supply of an ostensibly famous beverage made from herbs, grain and berries (I know, what kind of man drinks berry drinks?!?). And to the reader’s complete astonishment, the theologian accepts the offer, leaves hearth and home, and works side by side with the clerk to achieve theological balance and profundity once again. He even drinks the berry beverage with a smile.
When I read the story, following Lewis, I put all of the author’s agendas aside, and simply basked in the beautiful picture of faithful friendship….
Lewis is nearly always right….