The main thing is that Aslan is always there. He's the albatross when they are lost in the darkness; don't they see a fleeting glimpse of a lion pass by them on Deathwater? Lucy makes him visible on the island of the Duffers. And he speaks to Caspian in the cabin of the ship ... Although they may not see him or know he is there, still he is. It makes me think of these recent revelations about Mother Theresa, that in her final years she could not feel God's presence ... yet she kept on following Him and doing as He had commanded, just as if he were there. And I believe he was. and is.
I'd agree with you inkspot for VDT specifically. In my mind the theme for all the Chronicles is found in VDT at the end...but you'll find those words in my siggy.
Yes, I would say so. It also seems like difrent temptations are delt with on each Island. For example, pride was looked at in the land ofthe differs, the sin of greed on Deathwatwer.