For readers new to Narnia, publication order introduces, but chronological order confuses.
C.S. Lewis’s Chronicles of Narnia are sold in chronological order now, and have been for twenty years. But for the first forty+ years of their existence, they were sold in publication order, at least in America.
Why did Harper Collins change things? Because of a letter in which C.S. Lewis agrees with a young fan named Laurence that he prefers reading his books in chronological order. Here is a snippet of that letter. You can read more here.
I think I agree with your [chronological] order for reading the books more than with your mother’s [publication]. The series was not planned beforehand as she thinks. When I wrote The Lion I did not know I was going to write any more. Then I wrote P. Caspian as a sequel and still didn’t think there would be any more, and when I had done The Voyage I felt quite sure it would be the last, but I found I was wrong. So perhaps it does not matter very much in which order anyone read them. I’m not even sure that all the others were written in the same order in which they were published.
So, three things.
First, that’s an awfully tepid endorsement to base a major reordering of a well-loved series on.
Second, Lewis was corresponding with a child. If he had wanted to change the order of his series, he would have sent a letter to his publisher, or done something public that wouldn’t have remained hidden from the world until decades after his death.
And third, and perhaps most importantly, Lewis was talking to a fan who had already read the books multiple times, and had developed a favorite order for reading them that was different from the “pronounced order” at the time. Lewis was engaging with fandom, not a newbie, to use 21st century language.
This is a vital distinction. The Lion, the Witch, and the Wardrobe is written as an introduction to the world of Narnia. It is clearly and self-consciously the first book in a series, designed to stand alone if no more were published, and to serve as an introduction if the follow-up books happened.
The Magician’s Nephew is just as clearly written as a fan’s book. If you’ve gotten six books in, you like and know the series. You don’t need any explanation as to who Aslan is, or what Narnia is, or any of that. It’s clearly written in the form of a prequel. Sticking it at the front of the boxed set doesn’t change that.
Imagine if you’d never seen anything related to Star Wars, but you’d heard it was good. Then imagine your first introduction to the universe was The Phantom Menace. Well, it’s not quite the same, because The Magician’s Nephew is actually good. It’s also not quite the same as reading Harry Potter and the Half-Blood Prince first, either.
But it’s not much better, and I honestly believe that Narnia newbies reading the Chronicles in chronological order is responsible for the decline in the series’s prominence in the last couple of decades.
Now, for established fans, I think it can be fun to go back and reread The Chronicles of Narnia in chronological order. It gives you a fresh look into the series, after all.
But everybody who is new to Narnia should start with The Lion, the Witch, and the Wardrobe.