From Albert M. Wolters' Creation Regained:

Christians of virtually every persuasion have tended to understand "world" to refer to a delimited area of the created order, an area that is usually called "worldly" or "secular" (from saeculum, the Latin rendering of aion), which includes such fields as art, politics, scholarship (excluding theology), journalism, sports, business, and so on. In fact, to this way of thinking, the "world" includes everything outside the realm of the "sacred," which consists basically of the church, personal piety, and "sacred theology." Creation is therefore divided up neatly (although the dividing line may be defined differently by different Christians) into two realms: the secular and the sacred.

This compartmentalization is a very great error. It implies that there is no "worldliness" in the church, for example, and that no holiness is possible in politics, say, or journalism. It defines what is secular not by its religious orientation or direction (obedience or disobedience to God's ordinances) but by the creational neighborhood it occupies. Once again, it falls prey to that deep-rooted Gnostic tendency to depreciate one realm of creation (virtually all of society and culture) with respect to another, to dismiss the former as inherently inferior to the latter.

The tendency is a serious matter and has far-reaching consequences. Consider how it affects our reading of Scripture. When we read Christ's words "my kingdom is not of this world," many of us are inclined to understand it as an argument against Christian involvement in politics, for example. Instead, Jesus was saying that his kingship does not arise out of (Greek: ek) the perverted earth but derives from heaven. When James says that pure religion is to keep oneself unspotted from the world, we too easily read this as a warning against dancing or card playing or involvement in the dramatic arts on the grounds that they are simply "worldly amusements." But James is warning against worldliness wherever it is found, certainly in the church, and he is emphasizing here precisely the importance of Christian involvement in social issues. Regrettably, we tend to read the Scriptures as though their rejection of a "worldly" life-style entails a recommendation of an "otherworldly" one.

This approach has led many Christians to abandon the "secular" realm to the trends and forces of secularism. Indeed, because of their two-realm theory, to a large degree, Christians have themselves to blame for the rapid secularization of the West. If political, industrial, artistic, and journalistic life, to mention only these areas, are branded as essentially "worldly," "secular," "profane," and part of the "natural domain of creaturely life," then is it surprising that Christians have not more effectively stemmed the tide of humanism in our culture?