What is holiness?It refers to the essence of God's being, not so much a single attribute but perhaps the sum of all attributes.
Holiness suggests the power of God's presence (as when God appeared to Moses on Sinai), the “glory” (Greek: doxa) or aura of God's presence, the mystery of God when God is encountered, and the deep and hard-to-grasp nature of God as one who is both merciful and impatient with humanity, as one who has a special place in his heart for Israel and yet is God of all creation, as one who walks among the people and yet also awaits them on the mountain.
The holiness of God is both the majesty of God incarnate and the wonder of God beyond sight. Thus, one can walk into a “holy place,” like a quiet church, and feel caught up in something much larger than those walls and windows.
What is Holy? Let me suggest to you that holiness is not what you think it is. In theological terms we talk about holiness as being "set apart"—set apart for God. Even that, however, is a misunderstanding of the word. The actual root word is hool with "w" placed at the beginning, and it literally means whole. The simple duty of us all becomes nothing more, nothing less than becoming whole. Holiness is the process by which we integrate the loose threads of our life into a whole tapestry of beauty and divine grace. This is a creative task for the entirety of our lives. The Good News is that we can set aside all the to-do lists of things that we think are required for reaching some standard of moral and spiritual perfection, and open ourselves instead to the invitation and creative possibility of becoming whole in God.