Why did I never read this thread before? What lovely thoughts and ideas, and discussion of related and possible source writings!

One thing not suggested about the Wood and its pools is a link with another world Lewis wrote of: the fresh and unspoilt world of Perelandra, in Voyage To Venus. It too has water as an important part of the landscape, although in a different way. 

Sorry, I have the gift of the gab and this has turned into an essay rather than a simple comment 😳 

I don't know what 'the wood between the world', Charn or the rings mean as such, however I had a few thoughts to share that hopefully are helpful.

1. Repeated theme of deception / temptation / manipulation.

   In the first chapter of the book, Digory and Polly travel through an in-between place (Polly's tunnel through the rafters) to Uncle Andrew's Forbidden Study. Later, Digory and Polly travel through an in-between place (the Wood between the worlds) to Charn.

   When they see the door to Uncle Andrew's study, Digory asks if he should try it and Polly says, “I'm game if you are”. Just before they jump into the pool to Charn, Polly says, “I'm game if you are” once again.

   In Uncle Andrew's forbidden study, Uncle Andrew tricks Polly into touching the yellow ring. In this section, he behaves like a serpent, deceiving Polly:

   “
   ... “Wouldn’t you like a ring, my dear?” said Uncle Andrew to Polly.

   “Do you mean one of those yellow or green ones?” said Polly. “How lovely!”

   “Not a green one,” said Uncle Andrew. “I’m afraid I can’t give the green ones away. But I’d be delighted to give you any of the yellow ones: with my love. Come and try one on.”

   Polly had now quite got over her fright and felt sure that the old gentleman was not mad; and there was certainly something strangely attractive about those bright rings. She moved over to the tray.

   “Why! I declare,” she said. “That humming noise gets louder here. It’s almost as if the rings were making it.”

   “What a funny fancy, my dear,” said Uncle Andrew with a laugh. It sounded a very natural laugh, but Digory had seen an eager, almost a greedy, look on his face.

   “Polly! Don’t be a fool!” he shouted. “Don’t touch them.” ...
   ”

   Although this is not exactly a 'temptation' (as Polly is not doing anything wrong, she just wants to receive a beautiful ring that an apparently kindly gentlemen is offering to give her), Uncle Andrew is deceiving her to make her do something dangerous.

   Once Digory and Polly enter Charn, they encounter the bell on the square pillar. This time it is Digory who allows himself to be deceived into believing that he is fated to go mad unless he strikes the bell. We later find out that it is Jadis who is responsible for the bell:

   “
   “I had already cast strong spells on the hall where the images of my ancestors sit. And the force of those spells was that I should sleep among them, like an image myself, and need neither food nor fire, though it were a thousand years, till one came and struck the bell and awoke me.”...
   ”

   Initially it is Uncle Andrew who uses others to get whatever he wants without any care for them:
   “
   ... “I knew,” he went on, “that if only you could get it into the right form, that dust would draw you back to the place it had come from. But the difficulty was to get it into the right form. My earlier experiments were all failures. I tried them on guinea-pigs. Some of them only died. Some exploded like little bombs—”

   “It was a jolly cruel thing to do,” said Digory who had once had a guinea-pig of his own.

   “How do you keep getting off the point!” said Uncle Andrew. “That’s what the creatures were for. I’d bought them myself. ...
   ”

   And this selfish cruelty applies to the children whom he uses:

   “
   “But Polly hasn’t gota green ring.”

   “No,” said Uncle Andrew with a cruel smile.

   “Then she can’t get back,” shouted Digory. “And it’s exactly the same as if you’d murdered her.”

   “She can get back,” said Uncle Andrew, “if someone else will go after her, wearing a yellow ring himself and taking two green rings, one to bring himself back and one to bring her back.”

   And now of course Digory saw the trap in which he was caught: and he stared at Uncle Andrew, saying nothing, with his mouth wide open. His cheeks had gone very pale. ...
   ”

    

   In Charn, Jadis shows the same cruelty to her own people:

   "
   ... Then I spoke the Deplorable Word. A moment later I was the only living thing beneath the sun.”

   “But the people?” gasped Digory.

   “What people, boy?” asked the Queen.

   “All the ordinary people,” said Polly, “who’d never done you any harm. And the women, and the children, and the animals.”

   “Don’t you understand?” said the Queen (still speaking to Digory). “I was the Queen. They were all my people. What else were they there for but to do my will?” ...
   ”

    

   She too uses Digory and Polly as means to achieving her will:

    

   “
   Now that she was left alone with the children, she took no notice of either of them. And that was like her too. In Charn she had taken no notice of Polly (till the very end) because Digory was the one she wanted to make use of. Now that she had Uncle Andrew, she took no notice of Digory. I expect most witches are like that. They are not interested in things or people unless they can use them; they are terribly practical. ...
   ”

Both Uncle Andrew and Jadis justify their actions by saying “Our's is a high and lonely destiny!”

There may be a further repetition later in the book when Digory and Polly come to the garden. Here, though there are a number of clear changes:

Digory and Polly travel on Fledge rather than travelling through an in-between place to get to their destination.

Only Digory enters the garden, Polly does not come with him. While the garden is foreboding, Digory is explicitly commanded to enter it by Aslan.

Digory is warned before he is tempted in the garden by the writing on the gate.

This time, when Jadis attempts to deceive Digory, Digory resists and refuses to take the apple that Jadis offers.

Even though there are so many differences in the third temptation, I read this as the completion of Digory's arc where he learns to trust Aslan, rather than simply rely on himself.

1. 1. 2. I think there's also a deliberate contrast between the Wood Between The Worlds and Charn.

The wood between the world is a quiet, living place while Charn is a quiet dead place:

“
He was standing by the edge of a small pool—not more than ten feet from side to side—in a wood. The trees grew close together and were so leafy that he could get no glimpse of the sky. All the light was green light that came through the leaves: but there must have been a very strong sun overhead, for this green daylight was bright and warm. It was the quietest wood you could possibly imagine. There were no birds, no insects, no animals, and no wind. You could almost feel the trees growing. The pool he had just got out of was not the only pool. There were dozens of others—a pool every few yards as far as his eyes could reach. You could almost feel the trees drinking the water up with their roots. This wood was very much alive. ...
”

“
This place was at least as quiet as the Wood between the Worlds. But it was a different kind of quietness. The silence of the Wood had been rich and warm (you could almost hear the trees growing) and full of life: this was a dead, cold, empty silence. You couldn’t imagine anything growing in it.
”

The Wood Between the Worlds, is filled with nature: pools, grass and trees. While Charn contains only the ruins of man-made buildings:

“
And there were no ants or spiders or any of the other living things you expect to see in a ruin; and where the dry earth showed between the broken flagstones there was no grass or moss.
”

I struggle to get my head around why the contrast, but I feel like 'the deplorable word' would have no effect in the Wood Between the Worlds, Jadis is powerless there and she becomes weak and feeble. Whereas in Charn, Jadis is able to destroy the entire world.

3. I do not think Charn is allegorical for hell, but Jadis seems to be living in a 'hell' as described by Lewis elsewhere.

In “The Problem of Pain”, Lewis describes how people can end up with hell by their own choice:

“
... in creating beings with free will, omnipotence from the outset submits to the possibility of such defeat. What you call defeat, i call miracle: for to make things which are not itself, and thus to become, in a sense, capable of being resisted by its own handiwork, is the most astonishing and unimaginable of all the feats we attribute to the deity. i willingly believe that the damned are, in one sense, successful, rebels to the end; that the doors of hell are locked on the inside. i do not mean that the ghosts may not wish to come out of hell, in the vague fashion wherein an envious man “wishes” to be happy: but they certainly do not will even the first preliminary stages of that self abandonment through which alone the soul can reach any good. they enjoy forever the horrible freedom they have demanded, and are therefore self enslaved: just as the blessed, forever submitting to obedience, become through all eternity more and more free.
”

I relate to this passage a lot. When I was a child, my parents would send me to my room for misbehaving (usually because I had hit a sibling or done something equally bad). When I was waiting in my room, I could hear my brothers and sister playing outside and having fun while I was miserable in my room. I knew that I could come out at any time if I just admitted that what I had done was wrong and say that I was sorry. However, I would be in my room for a long time because as long as I stayed, miserable, in my bed room I had 'won' and my parents had 'lost'. My stubbornness in not wanting to submit would keep me unhappy for far longer than I needed to be punished. My punishment was ultimately of my own making.

C.S. Lewis also says in the same chapter:

“
.... but, of course, though Our Lord often speaks of Hell as a sentence inflicted by a tribunal, He also says elsewhere that the judgement consists in the very fact that men prefer darkness to light, and that not He, but His “word”, judges men. We are therefore at liberty — since the two conceptions, in the long run, mean the same thing — to think of this bad man’s perdition not as a sentence imposed on him but as the mere fact of being what he is. the characteristic of lost souls is “their rejection of everything that is not simply themselves”. Our imaginary egoist has tried to turn everything he meets into a province or appendage of the self. the taste for the other, that is, the very capacity for enjoying good, is quenched in him except in so far as his body still draws him into some rudimentary contact with an outer world. death removes this last contact. He has his wish — to live wholly in the self and to make the best of what he finds there. and what he finds there is Hell.
”

This is exactly what Jadis experiences in Charn. She sees all people as only existing to be 'her people'. They are essentially just slaves and mere human resources in the service of Jadis. She has made herself god and made everything else into merely an extension of herself. Thus it is nothing for her to speak the deplorable word and end all life. But Charn is left dead with nothing alive except Jadis herself. The place is lonely, lifeless and Jadis has nothing left to rule. So she casts spells for someone to wake her at which point she can repeat the same folly in a new world. Jadis is living Lewis's description of hell.

Later in the book Aslan essentially says the same thing Lewis said in The Problem of Pain:
“
... “It will. Things always work according to their nature. She has won her heart’s desire; she has unwearying strength and endless days like a goddess. But length of days with an evil heart is only length of misery and already she begins to know it. All get what they want; they do not always like it.”
”

If there is any ultimate meaning to The Wood Between the Worlds and Charn, I really think it is a prelude to the garden at the end of the book. Jadis chooses to make herself a god and ultimately lives in misery. She tempts Digory to do the same.

The narrative in the garden echoes Genesis 3, where Adam and Eve are tempted to eat a fruit for a tree known as “The Tree of Knowledge of Good of Evil”. 'Knowledge of Good and Evil' appears to be a Hebrew idiom. In Deuteronomy 1:39 and Isaiah 7:15 we find out that children do not yet have 'knowledge of good and evil". In 2^nd Samuel 19:35 we find that retired elderly no longer have "knowledge of good and evil". In 1^st Kings 3:9 God asks Solomon what he desires and is very happy when Solomon says that he needs "knowledge of good and evil" in order to rule Israel. God has "knowledge of good and evil" (in Genesis 3:22). The best explanation from the evidence has been suggested that the idiom refers to the maturity which frees one from being dependent on another. I.E. Retired people would be said to not have "knowledge of good and evil" because they were dependent on their children who took care of them in their old age, children depend of the parents, but a king needs such independence to rule well over their land. In Genesis 3, 'knowledge of good and evil' would thus refer to taking matters into our own hands rather than depending on God as a loving father to ultimately look after us.

Lewis seems to echo this idea in his book “Perelandra” as part of the Ransom trilogy:

In a conversation between the Ransom, the Green lady and the demon-possessed Western, we hear Western saying:
"
... “That is true of all His commands except one.”

“But can that one be different?”

“Nay, you see of yourself that it is different. These other commands of His — to love, to sleep, to fill this world with your children — you see for yourself that they are good. And they are the same in all worlds. But the command against living on the Fixed Island is not so. You have already learned that He gave no such command to my world. And you cannot see where the goodness of it is. No wonder. If it were really good, must He not have commanded it to all worlds alike? For how could Maleldil not command what was good? There is no good in it. Maleldil. Himself is showing you that, this moment, through your own reason. It is mere command. It is forbidding for the mere sake of forbidding.”

“But why…?”

“In order that you may break it. What other reason can there be? It is not good. It is not the same for other worlds. It stands between you and all settled life, all command of your own days. Is not Maleldil showing you as plainly as He can that it was set up as a test — as a great wave you have to go over, that you may become really old, really separate from Him.”

...

“Lady,” said Ransom, “if I speak, will you hear me?”

“Gladly, Piebald.”

“This man has said that the law against living on the Fixed Island is different from the other Laws, because it is not the same for all worlds and because we cannot see the goodness in it. And so far he says well. But then he says that it is thus different in order that you may disobey it. But there might be another reason.”

“Say it. Piebald.”

“I think He made one law of that kind in order that there might be obedience. In all these other matters what you call obeying Him is but doing what seems good in your own eyes also. Is love content with that? You do them, indeed, because they are His will, but not only because they are His will. Where can you taste the joy of obeying unless He bids you do something for which His bidding is the only reason? When we spoke last you said that if you told the beasts to walk on their heads, they would delight to do so. So I know that you understand well what I am saying.”

“Oh, brave Piebald,” said the Green Lady, “this is the best you have said yet. This makes me older far: yet it does not feel like the oldness this other is giving me. Oh, how well I see it! We cannot walk out of Maleldil’s will: but He has given us a way to walk out of our will. And there could be no such way except a command like this. Out of our own will. It is like passing out through the world’s roof into Deep Heaven. All beyond is Love Himself. I knew there was joy in looking upon the Fixed Island and laying down all thought of ever living there, but I did not till now understand.”  ...
”

Later, when the conflict is resolved, the Green Lady understands furthermore that she is called to trusting obedience and that there is joy in being obedient to one we can trust:

“
...The reason for not yet living on the Fixed Land is now so plain. How could I wish to live there except because it was Fixed? And why should I desire the Fixed except to make sure — to be able on one day to command where I should be the next and what should happen to me? It was to reject the wave — to draw my hands out of Maleldil’s, to say to Him, ‘Not thus, but thus’ — to put in our own power what times should roll towards us… as if you gathered fruits together today for tomorrow’s eating instead of taking what came. That would have been cold love and feeble trust. And out of it how could we ever have climbed back into love and trust again?”

”

I could be wrong, but I think Digory is on the same journey in the Magician's Nephew. He is tempted to seize a way of making his mother well, but he has to trust Aslan that Aslan is loving and that he really wants what is best for Digory. After Digory refuses to steal the fruit to give to his mother, it says:

“
He was very sad and he wasn’t even sure all the time that he had done the right thing; but whenever he remembered the shining tears in Aslan’s eyes he became sure.
”

And if you bothered to read all the above - thanks for letting me waste your time.  Feel free to disagree and put me in my place 🙂