If you're looking at the religious allegory in them, it's important to read them chronologically as well. The first book tells the creation by God, Aslan.
This second book, Aslan arrives and everything about him represents Jesus. Knowing what I know about these books and about CS Lewis makes this story that much better.
I especially love the way he describes Aslan, both before we meet him, and when we do finally get to see him take form.
"Then isn't he safe?" said Lucy.
"Safe?" said Mr Beaver; "don't you hear what Mrs Beaver tells you? Who said anything about safe? 'Course he ain't safe. But he's good. He's the king, I tell you."
That is the perfect picture of Jesus. All powerful, dangerous.. but also good. Then you meet Aslan.
"... when they tried to look at Aslan's face they just caught a glimpse of the golden mane and the great, royal, solemn, overwhelming eyes; and then they found they couldn't look at him and got all trembly."
That is almost exactly how John describes Jesus in the book of Revelation. He describes him as so holy, so glorified that when John sees him he falls over as if a dead man. So Aslan has come, Aslan has died, Aslan has risen.
I'm so excited to start the Horse and His Boy, I don't know if I want to wait until tomorrow.