Becoming Closer
The Call to Leave
nTension of the Remnant
nCalled Out
•Sodom
•Korah
•Matthew 24:15-16
•2 Corinthians 6:17
nHoliness
•Romans 12:2
There is a fundamental tension between the “Remnant”  -- those who have been faithful to God, not those who merely go to church -- and the world system.  The remnant hears the voice out of heaven (Jesus?) and comes out.
It has been so since Abraham;  Lot was called out of Sodom.  At the rebellion of Korah against Moses (Numbers 16:26-28) Moses told the people to step back (or get fried).  Jesus commands the same at the abomination of Daniel (Matthew 24:15-16).
The principle is found here:
(2 Cor 6:17 NIV)  "Therefore come out from them and be separate, says the Lord. Touch no unclean thing, and I will receive you."

Holiness.  The idea is that of separation.  The separation is not necessarily physical (though in this instance it may well be a good idea!) but it certainly is mental:
(Rom 12:2 NIV)  Do not conform any longer 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.

{Side note:  this passage is fertile ground for grand conspiracy theorists;  see Chuck Smith on the subject}