The first line of Charlotte’s Web is about preventing a murder. “Where’s Papa going with that ax?” Fern asks her mother. When she learns that he’s going to the hoghouse to kill the runt of a litter born the night before, she chases her father down and talks him out of it. “This is the most terrible case of injustice I ever heard of,” she says.

That note of urgency, and farm life realism, courses through the book, giving it the energy that has made it such an eternally beloved, indispensable classic. Now we know that’s just what E.B. White, the author, intended. In a letter to his editor, Ursula Nordstrom, written in September 1952, a few weeks before the book was published, and posted recently on Letters of Note, White wrote:

A farm is a peculiar problem for a man who likes animals, because the fate of most livestock is that they are murdered by their benefactors. The creatures may live serenely but they end violently, and the odor of doom hangs about them always. I have kept several pigs, starting them in spring as weanlings and carrying trays to them all through summer and fall. The relationship bothered me. Day by day I became better acquainted with my pig, and he with me, and the fact that the whole adventure pointed toward an eventual piece of double-dealing on my part lent an eerie quality to the thing. I do not like to betray a person or a creature, and I tend to agree with Mr. E.M. Forster that in these times the duty of a man, above all else, is to be reliable. It used to be clear to me, slopping a pig, that as far as the pig was concerned I could not be counted on, and this, as I say, troubled me. Anyway, the theme of “Charlotte’s Web” is that a pig shall be saved, and I have an idea that somewhere deep inside me there was a wish to that effect.

White also defended spiders—in particular, Charlotte’s real-life namesake, whom he watched spin a sac for her eggs at his place in the country, and then toted off to New York:

A few days later, when it was time to return to New York, not wishing to part with my spider, I took a razor blade, cut the sac adrift from the underside of the shed roof, put spider and sac in a candy box, and carried them to town. I tossed the box on my dresser. Some weeks later I was surprised and pleased to find that Charlotte’s daughters were emerging from the air holes in the cover of the box. They strung tiny lines from my comb to my brush, from my brush to my mirror, and from my mirror to my nail scissors. They were very busy and almost invisible, they were so small. We all lived together happily for a couple of weeks, and then somebody whose duty it was to dust my dresser balked, and I broke up the show.

White ends by saying that he hasn’t told Nordstrom why he wrote the book “but I haven’t told you why I sneeze, either. A book is a sneeze.” It’s a delightful metaphor. But in fact, I think White has told us why he wrote Charlotte’s Web. He wanted to make children, and their parents, think about what it means to raise animals only to butcher them. And why we should consider letting that spider in our bedroom live.