A friend of mine asked me to give them a few thoughts on Christian holiness...I thought I would post those "random" thoughts here:
Holiness is Christlikeness. Biblically...holiness, sanctify, sanctification means "to be set apart." Holiness means we are set apart for God's use, but it always has a moral (behavioral) aspect. God's work in our lives means that we act as though we are the people of God.
The Israelites were given the 10 Commandments not as a way of "saving" them through works. They never believed they could earn their salvation by obeying the Law. They obeyed the Law because God had chosen them and that is how God expected His people to act. We are to live lives of holiness and moral purity because we are God's people...not because it will earn our way into salvation or give us better standing with God.
Holiness is in complete reliance on grace, but not a cheap grace. Holiness needs grace because we cannot be holy without God's gift of grace. But we also cannot be holy without a healthy respect and understanding of sin as something that hurts, destroys, and kills God's good creation. True holiness comes as a result of understanding the depth and destruction of our sin, but also the power of God's grace to forgive and help us live above sin. I am not saying that we live an absolute sinless life (see the next few paragraphs). But we don't willful sin against God by doing something we know to be wrong, and we seek forgiveness when we realize that we have sinned and didn't know it.
Another aspect of holiness is perfection. There are two ways to think of perfection. The most common, and most non-biblical, is the standard Western definition of perfection that Christianity picked up from the Greek philosophical mindset. That definition is complete and utter perfection. Nothing broken, nothing wrong, nothing sinful, no flaws...absolute perfection.
The second definition of perfection is the biblical, Hebraic one. That is the perfection of maturity...or an improvable perfection. It refers to a "fitness for use." An example that I use is one of development. A two year old who babbles, sucks his thumb, and needs a diaper is still a "perfectly good" two-year-old. A 25 year old who does those things has developmental problems. That is a rather dramatic example, but reminds us that if we can say "perfection" is not an absolute perfection, but one of being where we are supposed to be developmentally in our spiritual walk.
Leviticus 11:44, "I am the LORD your God; consecrate yourselves and be holy, because I am holy."