Reflect on Genesis 3. What did Satan do in the Garden of Eden? He promoted disbelief of God, and this lies at the root of the difference between us and those in the world, whom Paul characterizes as turning from the truth.
Can a person be a Christian without believing? Can a Christian pick and choose what to believe and what not to believe? Satan has deceived the whole world (Revelation 12:9), and he deceives by subtly promoting disbelief of God's Word. It is so simple. And there it is, brought to our attention right at the very beginning of the Book. It is related so very simply to help us understand a principle that can be the foundation of great understanding and insight.
In Genesis 3, God clearly shows what delineates His people from the world. What Adam and Eve did was lay the foundation of the world. The world as we now see it, with all its cultures and all of its political, educational, economic, business and religious systems, grew or was built following the same general pattern of disbelief in what God said. Our world contains that same general pattern of good and evil—some from God, some from Satan.