The context of this quote is that the characters of the story have been in a dinghy for several days. They are close to land, but they are unable to get inshore. Essentially, they are beginning to confront (at least internally) the prospect that they may not survive, a reality that is portrayed rather bluntly by the fact that a shark is beginning to circle around the boat. This passage, then, reflects the sheer unimportance of four men amid the vastness of nature. This is difficult for people to understand, as we are inherently self-centered. But we are powerless, or at least very weak, before nature, and our lives mean little in the grand scheme of things. They are only important to us.