The alleged allegory Christians insist on breaks down when Aslan (the supposed Christ figure) accepts a person who worshiped Nash (the supposed Satan figure). Aslan imputes the person's lifelong worship of Nash to himself (universalism). Aslan also endorses and encourages Lucy to cast spells, and refers to the "magic" which he and all of Narnia is supposedly subject to. Aslan doesn't die for everyone--he only dies for Edmund--implying that the rest don't need forgiveness/a sacrifice.
But it isn't an allegory.
The episode with Emeth in the last battle has perplexed a few people (and it perplexed me for a bit too till I remembered its a story not a systematic theology) So perhaps because of trying to use Narnia as a theological source to see if it matches up with the Bible people get into difficulties. But failing to
read it as a story seems to be were most go wrong.
Emeth (whose name means truth) in
The Last Battle is converted
on the Purlieus, as it were of the New Narnia
, because he was in the world of the story a truth seeker, and sought truth even when it meant he might lose his life.
When he meets Aslan he falls down and worships Him, confessing he had all his days worshipped Tash. Aslan forgives him and tells him nothing vile can be done in service to him, and nothing that is not vile can be done in service to Tash, and that unless his desire had been for Aslan, he would not have sought so long and so truly, for all find what they truly seek. Clearly Emeth is representative of noble truth seekers.
Emeth has refused to worship the false and syncretic Tashlan, that Shift the Ape has set up to deceive the Narnians. Suspecting it to be a lie, Though not a Narnian he lived up to the only truth he knew.
On the other hand Rishda Tarkann who called on Tash, because he wants to make use of Tash for his own selfish ends, doesn't get into the New Narnia, and neither do the Dwarves who were only out for themselves. If I recall correctly Rishda doesn't expect to meet Tash, and when he does Tash picks him up with its beak, before Peter banishes Tash, saying something like "Begone Monster, and take thy lawful prey with you".
Emeth was a believer who was prepared to face Tash even if Tash should slay him, Rishda was an unbeliever.
There is a clear separation at the end of the Last Battle based on the creatures response to Aslan as they walk up to him, either love or hate. Not everyone enters the New Narnia. Lewis therefore was inclusivist in his views,
but not universalist.