In 'The Great Divorce' a character asks, destraught, why she was born and a spirit replies, "for infinite joy!" Is that what CS Lewis thought the meaning of life was? Ultimate joy? Is there any other thing he said to back up this idea of what he thought? It would seem odd if such a clever, philosophical man (in my opinion) ignored the BIG 'meaning of life' question entirely!
tl;dr> NO! For Lewis, Pleasure is temporary, Joy reminds us of what is to come
First and foremost, I should admit that if the canon ever gets re-opened, The Great Divorce is my vote for book #67. :)
That said, C.S. Lewis has a very definite idea in mind when he says "Infinite Joy". In The Weight of Glory he writes:
“It would seem that Our Lord finds our desires not too strong, but too weak. We are half-hearted creatures, fooling about with drink and sex and ambition when infinite joy is offered us, like an ignorant child who wants to go on making mud pies in a slum because he cannot imagine what is meant by the offer of a holiday at the sea. We are far too easily pleased.
Contrast this with mere "pleasure" when Lewis writes in Chapter 9:
"Then is no one lost through the undignified vices, Sir? Through mere sensuality?"
"Some are, no doubt. The sensualist, I'll allow ye, begins by pursuing a real pleasure, though a small one. His sin is the less. But the time comes on when, though the pleasure becomes less and less and the craving fiercer and fiercer, and though he knows that joy can never come that way, yet he prefers to joy the mere fondling of unappeasable lust and would not have it taken from him. He'd fight to the death to keep it. He'd like well to be able to scratch: but even when he can scratch no more he'd rather itch than not."
Joy is the end - the purpose - of what God designed us to be. He sees joy as an "echo of heaven" which "works its way backwards into our memories." In other words, it is a reminder of the things that are to come.
As he says in The Weight of Glory (again):
The books or the music in which we thought the beauty was located will betray us if we trust to them; it was not in them, it only came through them, and what came through them was longing. These things—the beauty, the memory of our own past—are good images of what we really desire; but if they are mistaken for the thing itself they turn into dumb idols, breaking the hearts of their worshippers. For they are not the thing itself; they are only the scent of a flower we have not found, the echo of a tune we have not heard, news from a country we have never yet visited.
This idea - that joy is an echo of heaven is more thoroughly developed here, and is often referred to as Sehnsucht.