What Does it Mean to be Worldly?

Aaron Blumer recently posted the second part of an excellent series (Part I here) answering the question "What Does Worldly Look Like?" For many believers, abstaining from worldiness means just doing the opposite of whatever is popular, stylish, or mainstream among non-Christians but Aaron demonstrates how this notion is both biblically and logically unwarranted. Certain forms of worldliness may, in fact, be popular but what is popular is not necessarily worldly.

Concerning the reasons for the confusion over what "worldly" means, Aaron says:

The most important for our purposes is that the meaning of “worldly" depends on the meaning "the world," and many are confused regarding what "the world"” means. What exactly is it that disciples of Christ should not be “like"? How much does it have to do with garments, music, hairstyles, or theaters?

These posts called to mind one of the most memorable definitions of worldliness I've come across. It's from David Wells's book, Losing Our Virtue: Why the Church Must Recover Its Moral Vision:

Worldliness is that system of values, in any given age, which has at its center our fallen human perspective, which displaces God and his truth from the world, and which makes sin look normal and righteousness seem strange. It thus gives great plausibility to what is morally wrong and, for that reason, makes what is wrong, seem normal.