I liked the entry for January 9th in the book Heart of the Matter:
I Corinthians 1:18-25
The world bears the mark of sin. Culture provides a way for us to see ourselves and the world. It emerges whenever people gather together. Therefore, families, schools, and church denominations all have particular cultures. Culture oversees the unwritten guidelines for manners, traditions, and relationships: whether or not we have dinner together, how we celebrate our holidays, whether we raise hands in worship or kneel, how we greet each other, and so on.
Infused through culture, however, is what Scripture refers to as the world. The world was created by God as the abode of human beings. As created by God it is good, but as our abode it bears the mark of our sin. Therefore, in the New Testament, the term world is used to denote the order of things that are alienated from God. In this sense, it is morally corrupt (2 Peter 1:4), peddling foolishness as wisdom (I Corinthians 1:20) and interpreting God's wisdom as foolishness (I Corinthians 1:23). Even though we don't need any assistance in sensual indulgence, the world plants the message that unbridled sensuality is good, thus abetting the tendencies of our own hearts.
Recognizing that the world is outside us heightens our awareness of the spiritual battle we must fight. Not only do we have to fight against our own sin, we also have to fight against aspects of the culture that applaud our sinful tendencies rather than rebuke them.