Do not be conformed to this world, but be transformed by the renewing of your mind, that by testing you may discern the will of God, that which is good and acceptable and perfect. Romans 12.2
When I was a kid I envied my brother, Jeremy, for his artistic ability. The closest I could come to his creations was to trace other people's artwork. I confess that I even tried to pass off my traced work as originals. Of course, anyone who collected the Amazing Spider-Man series of comics had my number! A person can have some nice looking "artwork" by tracing, but you can't create something new by tracing others' works. Unfortunately, many Christians conduct their lives by tracing. Their conduct simply reflects the attitudes, beliefs and practices of the world of unbelievers around them. The choices they make and the actions they take are but carbon copies of the scheme of this world. This is what Holy Spirit calls us away from when He says, "Do not be conformed to this world."
The answer of course is not simply to avoid worldliness. Many Christians attempt to live this way and wind up very depressed because the "Christian life" is all about what I'm not doing. This Scripture gives the positive exhortation "be transformed." Transformation involves a new reality. John Owen points out that in the New Birth we are really transformed but not absolutely transformed. There is much transformation that takes place after regeneration. Thus Paul can speak of being "transformed into the same image (i.e., of Christ) from one degree of glory to another"; and state that "while our outer nature is wasting away, our inner nature is being renewed day by day" (2 Cor 3.18; 4.16). We might speak of this as the process of maturing by the grace of God, effectually working in us. It might be a good exercise to ask yourself whether you have matured spiritually in the past few months.
This transformation takes place, according to the Word of God, by the "renewing of your mind." Just as the New Birth is the work of the Spirit of God, this renewing of the mind is also the Spirit's work. Again, note what we possess really versus what we possess absolutely. On the one hand, Paul can say to the Corinthian Christians that "we have the mind of Christ" (1 Cor 2.16). On the other hand, Paul exhorts the Philippians to "let this mind be in you which was also in Christ Jesus" (Phil 2.5). Calling on Owen again, at the New Birth our minds were genuinely made new since we are "not in the flesh but in the Spirit" (Rom 8.9). Yet, God calls on us to have our minds "renewed" because they are not completely renewed. The Spirit continues this work of renewal by presenting Christ to our minds by the instrument of the word of God (see 1 Cor 2.6-16 for the Spirit's work in the Apostles' teaching; 2 Cor 3.12-18 with regard to the Old Testament, particularly).
The result of this renewal is that we might discern the will of God. We will discern what is the good, acceptable, and perfect way to think, feel, behave. Only in this way will we fulfill the exhortation of the first verse to present our whole person to God as a sacrifice, living, holy and pleasing.