Romans 12:2
Do not conform to the pattern of this world, but be transformed by the renewing of your mind. Then you will be able to test and approve what God's will is—his good, pleasing and perfect will.
Have you ever heard the phrase, “Think outside the box?”
This is Paul’s version.
Having a preconceived idea is sometimes the hardest part of thinking. It tends to have you thinking about the expected answer without looking at the situation clearly.
“If all you have is a hammer, everything you see looks like a nail.”
Paul is telling the Romans to be careful about being so closely conformed to the desires -- expectations -- values -- and traditions of this world. If they (or we) have the world in their (our) hearts, then it will be all too easy to rationalize -- justify -- excuse -- gloss over the times they (we) stray from God’s Will.