"So much" depends upon this particular red wheelbarrow. While we're not quite sure what exactly this "so much" is, we know it is more than a couple of rocks or a pile of dirt. "The Red Wheelbarrow" reminds us of the fact that a wheelbarrow was designed to be a tool thousands of years ago, and it remains a tool in the modern day. Its job is to help people build things, carry things, and create things. The wheelbarrow is a very dutiful object.
The wheelbarrow is vitally important and has many duties.