"We are not to be isolated but insulated," said Vance Havner, "moving in the midst of evil but untouched by it."
Separation is contact with contamination. Jesus was "holy, harmless, undefiled, separate from sinners" (Heb. 7:26), yet He was "a friend of tax collectors and sinners" (Luke 7:34).
(SOURCE: from a sermon by Mark Schaeufele, "Living in Christ Part 1: Off With the Old and On With the New" 7/28/08, http://www.sermoncentral.com/sermon.asp?SermonID=125035&Sermon Living In Christ Part 1: Off With the Old and On With the New by Mark Schaeufele)