Holiness is separation unto God and separation from (sin) the world, not isolation. We are in the world but not of the world, therefore we should not be influenced by the world - "Love not the world neither the things of the world, for if anyone love the world the love of the father is not in him." (1 John: 2 verse 15)
"But as he which hath called you is holy, so be ye holy in all manner of conversation. Because it is written, be ye holy; for I am holy." (1 Peter 1 verses 15 – 16)