In this video, Stephen Tong defines holiness.
Holiness is the basic nature of our God. And He is the only holy God, more holy than any other gods understood by other religious worship. So holiness is something that distinguished God from other false gods. And God is holy. He calls us to take part in His holiness. And by the fear of the Lord, we understand the holiness of God. And this is very important. If we are not holy, we cannot walk with God, we cannot do His will, and we cannot be accepted by God. God separates us from the sinful world, sinful environment, and also changes our sinful nature to be partakers of His own divine nature.