What is holiness?

The biblical concept of holiness is different than accomplishing a list of do's and don'ts.  Many believers try to adhere to a code of conduct by sheer will-power often placing vigorous external restrictions on themselves.  But that doesn't necessarily make them holy.  In fact, such moral achievement may lead us to a more insidious sin: pride!  Besides we know from experience that mere outward behaviour is inadequate; our internal struggles of greed, lust, anger, resentment etc. give us no peace of mind--we know we fall short internally even if we put up a good front on the outside.  

Specifically, holiness means to be set apart for a special purpose -- pleasing God.  

I Peter 2:9 tells us that believers in Jesus are 'a chosen people, a royal priesthood, a holy nation and a people belonging to God'.  Christians are set apart for God's purpose on the basis of our salvation through Jesus. This means that we have 'holy' status with God already because of Jesus; we are not set apart because we make ourselves holy: holiness is given to us.  

He graciously sets us apart and makes us pleasing to Himself.