Furniture scratching is a frustrating behavior unwelcome by most cat owners. In the cat's mind, he is simply marking his territory or sharpening his claws. For you, he is destroying an expensive piece of furniture. There are a couple of ways to diminish this behavior. The easiest, though painful for the cat, is declawing. A more humane method is behavior modification including the use of deterrents, periodic nail trims and training your cat to use a scratching post.
For more information, please read the story Furniture Scratching by Cats