A Book Case is a block that is only available from the Block Shop. It is about as durable as wood, but is really available for decorative purposes. The block clearly resembles a bookshelf as there are many books in various colors stacked together on each shelf of the block, however, none of these books can be interacted with currently.
Bookshelves can be crafted with 2 wooden planks and do not serve as a use for anything other than a form of decor. However, the 1.8 update features bookshelves (or bookcases as the developers stated) that act as storage for books, blueprints and wisdom scrolls.