There are several reasons why books are important, from serving as factual records of historical events and scientific discoveries to providing an outlet for artistic expression and creativity. Experts, including author Neil Gaiman, have argued strongly in favor of fiction books as being important tools, allowing readers to exercise their imaginations and general literacy skills. Books help foster literacy, which is an important skill for citizens to have so they can be politically and personally empowered to do things like vote, write to political representatives, understand rules and regulations regarding things like credit cards, and read employment contracts and other important legal documents.
Aside from their practical applications as tools of factual record and literacy, books are also important for preserving and transmitting stories. Storytelling is a human impulse that is a part of nearly every culture. In some cases, stories are passed down orally, but oral literary traditions rely on memorization and the health and safety of those who know the stories. Writing stories down and publishing them as books helps to ensure the endurance of these stories.
Now that digital books are becoming more popular, it can be argued that physical books have less importance. However, that doesn't mean that the content of books themselves, no matter what format they come in, is any less essential.