I come from a denomination bent on bringing holiness to the world. Unfortunately, I think they have confused the message of holiness with their particular method for how that holiness becomes part of a believer's life. So what happens is that when a person rejects their brand of holiness, they often reject the idea of holiness altogether.
I am a firm believer in the message of holiness. I believe that as God's followers He desires to make us into a holy people.
What do I think holiness is?
Holiness is simply Christlikeness.
This is connected to the Christian idea of sanctification. Sanctification is all that God does to bring us into living a Christlike life.
Jesus is our ultimate example. We are to model our lives after Jesus, and we are able to do this through the power of the Holy Spirit. We are told that the Fruits of the Spirit are love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, and self-control. These fruits should be part of our lives in an ever increasing measure.
Living the sanctified life (not to bring up the imagery of some denominational definitions) is a dangerous lifestyle. We are asked to change, develop, grow, and expand our boundaries of ministry (again, not in the harmful way of some understandings of the Prayer of Jabez). The sanctified life is one of radical, active love for God and neighbor. It means that we love justice, seek mercy, and walk humbly with our God.
Some doctrinal statements say that sanctification is a "definite second work of grace," or they say that it must be accompanied by the peson speaking in tongues. Or some say that it is completely process.
Sanctification is both process and event. By event I mean there are times when God in the Holy Spirit intersects our lives and we are dramatically changed. By process I mean these events can happen multiple times AND that God uses our worship, service, interaction in community, and spiritual disciplines to shape us into holy people. God is not a quick-fix god. He does not always change us in an instant. He can and does, but often, it seems, the transformation is in the long, slow, commitment to growth and closeness.