It is in one of his last letters (5 March 1961) to an older child, Anne, that Lewis most fully explains his intentions for the Chronicles of Narnia. Anne seems to have written Lewis about a scene from Chapter XVI, The Healing of Harms, in The Silver Chair. Aslan, Eustace, and Jill are in Aslans Country and they have just witnessed the restoration of the dead King Caspian to full life and youthful vigor. Jill cannot understand what she has just seen, so Aslan explains that Caspian had died and so had he.
"What Aslan meant when he said he had died is, in one sense plain enough. Read the earlier book in this series called The Lion, the Witch and the Wardrobe, and you will find the full story of how he was killed by the White Witch and came to life again. When you have read that, I think you will probably see that there is a deeper meaning behind it. The whole Narnian story is about Christ. That is to say, I asked myself Supposing that there really was a world like Narnia and supposing it had (like our world) gone wrong and supposing Christ wanted to go into that world and save it (as He did ours) what might have happened? The stories are my answers. Since Narnia is a world of Talking Beasts, I thought He would become a Talking Beast there, as He became a man here. I pictured Him becoming a lion there because (a) the lion is supposed to be the king of beasts; (b) Christ is called The Lion of Judah in the Bible; (c) Id been having strange dreams about lions when I began writing the work. The whole series works out like this.
"The Magicians Nephew tells the Creation and how evil entered Narnia.
The Lion etc the Crucifixion and Resurrection.
Prince Caspian restoration of the true religion after corruption.
The Horse and His Boy the calling and conversion of a heathen.
The Voyage of the 'Dawn Treader' the spiritual life (especially in Reepicheep).
The Silver Chair the continuing war with the powers of darkness.
The Last Battle the coming of the Antichrist (the Ape). the end of the world and the Last Judgement."