The quote captures Smith's description of the complexity and scope of the division of labor, and its ability to increase the standard of living in a given society. Smith believes that the propensity to truck, barter and exchange is part of human nature, and it is precisely this capacity that best organizes the economic system in large scale societies. The cooperation of the many thousands, inspired by each person's self interest, is what allows for the economic system to flourish, spreading opulence and raising the overall quality of life. Since observations on the progress inspired by the division of labor begin the book, Smith uses the contemplation of simple items (pins, for instance) as a starting point for his theorizing on the organization of economics in general.