Romans 12:2: And do not be conformed to this world, but be transformed by the renewing of your mind, so that you may prove what the will of God is, that which is good and acceptable and perfect.
So what does it mean to not "be conformed to this world?" Seems pretty important, since that is key to proving "the will of God..." - demonstrating "that which is good and acceptable and perfect."
Four Parts to this answer:
1) Part 1 is found in the verse right before this one - Romans 12:1. We are to daily present ourselves as "living sacrifices". We are to submit our will to His. The first step in not conforming to the world is that we conform to His will. Being a sacrifice means that we submit even in areas where we do not feel like it. We submit only because He calls us to. Sacrifice inherently implies that we give up what we want - otherwise it is not sacrifice. It means that our lives are not driven by our "feelings" - but by our commitment to Him - regardless of how we feel.
2) We recognize that we are aliens in this world. 1 Peter 2:11 says that "as aliens and strangers" we are "to abstain from fleshly lusts which wage war against the soul." We are not to love the things of this world. Yes we are "free in Christ" - but that freedom is
freedom from sin. We are still slaves - slaves to Christ. This world is not our home. So, we should always be careful to not abuse our "freedom in Christ" to justify making this world comfortable - to do anything that makes this world more "home-like". That is conforming to the world. Our lives should be marked by seperating from the world. Anything that betrays our true citizenship only puts us "undercover" - the antithesis of what Christ has called us to be. So, as we exercise freedom in making practical decisions, a driving question should always be - "does this decision more closely associate me with the world or with Christ?"
3) We exercise discipline. Somehow, many Christians today have decided that freedom in Christ means a freedom from discipline. But that is a foreign concept to the New Testament. Paul talks of "buffeting his body" with regard to discipline. There are 18 passages in the New Testament regarding how we are to discipline ourselves - or that God will discpline us. We are told to be discplined about study, doctrine, fasting, praying, giving, exercising spiritual gifts, refraining from certain activies, acting in others, use of judgement, etc. Many Christians will say, though, "What if I don't feel like doing something? Shouldn't I wait until my heart wants to first?" That's a lazy, unbiblical response. Jesus says that where our treasure is, there will our heart be also. We must put our treasure where we want our heart to be - before our heart is even necessarily there. That's what discpline is about. We do what God has called us to do. Because He's God. And we are not. Obdience is about volitional love. Not love based on what we "feel" - but love based on the fact that we decide to love and honor the Lord because we must - because of who He is - and that He has called us to love Him and honor Him as Lord. "Not being conformed to this world" requires a dicsipline to live and do as God calls - regardless of feeling. Conformity to the world is marked by a living by feelings.
4) Non-conformity to the world requires commitment to a local church. There is no such thing as a Christian outside of a local church in the New Testament. We are to not forsake the assembly of believers. Within the church we are to "stimulate one another to love and good deeds". We are to be as iron sharpens iron. The body of believers is to work toward pushing each individual towards being Christ-like. This likely means pain. But God uses that pain to sharpen us. But there is also joy, fellowship and love amongst believers that the world can never understand (Philippians 1). This pain, joy, love, etc. is all found within the local body through fellowship, service, and accountability - and draws us to our true citizenship, keeping us from conforming to this world.
Not conforming to this world is a conscious decision. We sacrifice our lives, we recognize we are aliens, we excercise discipline, and we subject ourselves to a local body of believers. God has so much for us beyond this life - why would we want to cling to this world anyway?