The main point of this story is that harmony among siblings is no less a struggle than the epochal battle between Good and Evil.
The problem faced by Lucy and her siblings (Peter, Susan, Edmund) is to deliver Narnia, the land they reached crossing the magic wardrobe, from the clutches of an evil White Witch. The problem is compounded when Edmund yields to the dark side for a fistful of sweets.
The resolution of the problem is brough about by the providential appearance of the lion-king, Aslan. His arrival enables the children, in turn, to do great deeds of their own.
The child appeal of this story is due to the reassuring, grandfatherly tone of the narrator--contrasting with the exciting dangers of an adventure of unusually epic proportions.
The parent/teacher appeal of this story is in its relentlessly moral message--unlike the somewhat amoral tone of many fairy tales, implicitly criticized just as their narrative devices are borrowed.
Notes for a book report
Pervasive Christian symbolism:
Aslan as Christ, the Stone Table shattering like the Holy Sepulcher to announce the resurrection. He is the accessible aspect of the trinity ("Us lions", inclusive of an ordinary feline), as opposed to the Father/Emperor-beyond-the-Sea, who remains distant.
Edmund, a traitor (more like St. Peter than Judas, the despairing one); but also--like the prodigal son--the one who returns and is forgiven.
The White Witch, a fallen angel intimately knowledgeable with the Deep Magic (which she uses for evil)--but ignorant of a critical passage. Like the snake in the Garden, she offers irresistible morsels to Edmund.
Obscure scriptural references (Lilith, Adam's first wife).
Tiny mice nibbling at Aslan's ropes: "And the Last Shall be First...", plus a reference to Aesop.
Giant Rumblebuffin is the same sturdy English peasant, paragon of rustic virtue, seen in many guises in Secret Garden. From today's vantage point, this has the uncomfortable feeling of upper-class condescension.
Another similarity between the two books is the theme of children exploring a vast mysterious old house.
Like all traitors, Edmund is, in the end, the most interesting of the four children. He goes from resentment, to gluttony and betrayal, to terror and pain, to a first inkling of empathy (when the fox and its guests are turned into stone), to repentance, to heroism (royally rewarded). A most grandiose riff on the basic theme of sibling rivalry.
Quest conventions common to this and other stories include:
A portal to another world--an ordinary-looking affair, as in Phantom Tollbooth. In both books, the portal can only be used once: after learning their lesson, the children have to do the hard work of leading a righteous life without reliance on magic.
Vivid details of the passage to the other world: here, the fur coats turning into snow-laden foliage; in Wrinkle in Time, the literally breath-taking experience of "tessering".
In each story, a generous mix of helpers (Professor, Beavers, Father Christmas), antagonists (the Witch and her henchcreatures), traitors (Mr. Tumnus at first, then Edmund).
Gifts, brought in this story by Father Christmas himself:
Sword and shield for Peter.
For Susan, a horn to call for help. She also gets a bow and arrows, but she is not to use them in battle because she is a girl.
For Lucy, a healing potion. She too gets a weapon (a dagger), and is forbidden to use it in battle on account of her gender.
As in Phantom Tollbooth and Wrinkle in Time, we see here too a dissatisfaction with conventional schooling. It's in the Professor's constant remarks ("What do they teach them?") and in Edmund being "twisted" by the school he attended.
Aslan takes on many other guises, in addition to the Christian ones:
He is a hero, but also a terrible god--the children must avert their gaze at his wrath.
Lucy's perception of him alternates between the playful kitten (when he romps with the two girls), and a thunderstorm (as he roars).
As a lion, a symbol of British royalty, he may also inject a nationalist tone in this story written soon after the end of World War II.
Compare to modern retellings of the same basic quest (such as Star Wars), which invariably require:
Lots of stuff to blow up.
Extra-special effects.
Generic non-denominational spiritual mumbo-jumbo, enough to draw a wide audience without offending any potential customers.
Class discussion themes
A quest similar to Wrinkle in Time: the heroes must recover a good character gone bad.
Influenced by the author's Christian beliefs, and the struggle against evil in WWII.
Use of animal characters, black magic instead of state brutality: helps introduce real-life evil (horrors of war and persecution) without shocking children outright.
The White Witch is a political oppressor--she usurps power
To war-weary English children in 1950, the wardrobe is an escape from the disruptions and grief in their lives.
The narrator directly addressing the reader regarding grief--helps children, who may have suffered losses in the war, accept their feelings (as well as drawing all readers into the story).
Main issue surrounding Aslan: why did he not come earlier? Which is the same as: why is evil allowed in the world?
The book's answer is that there is a season for harshness (the winter of the White Witch), and a season for hope (Aslan/Spring breathing life into the petrified victims of the Witch).
The professor is a guide, but one who grants children their independence--he won't do the hard work for them.
His matter-of-fact acceptance of the children's adventure suggests that he may have traveled through the wardrobe himself.
From a Christian perspective, he functions like a minister: whetever you believe in your heart, that is true.
Message for Edmund the unwary: don't take candy from strangers.
Lucy shows courage in sticking to her story in the face of disbelief.
Aslan teaches an important lesson for children when he forgives Edmund, and intimates that nobody should hold a grudge against him.