Order reflects the degree to which those with substantial power accept existing arrangements or rules for conducting international relations, as well as the diplomatic mechanisms for setting and modifying those rules. It also reflects the ability of those same powers to meet the challenges of others who do not share their perspective. Disorder, as explained by both Bull and Kissinger, reflects the ability of those who are dissatisfied with existing arrangements to change them, including through the use of violence.
-- Richard Haass (chapter 1 paragraph 2)

Importance: This describes the basic concept of world order, allowing the reader to understand Haass's later arguments. It also demonstrates its prominence in previous foreign policy scholarship.

The treaty was something of a breakthrough, in that disorder and conflict born of frequent interference inside the borders of one’s neighbors had been the norm. The Westphalian order is based on a balance of power involving independent states that do not interfere...
-- Richard Haass (chapter 1 paragraph 2)