You might be interested to know that the holiness of God is referred to more often than any other attribute. Thomas Watson once said, “Holiness is the most sparkling jewel of his crown; it is the name by which God is known.
When you see angels worshipping in heaven, they are not crying, “Mighty, mighty, mighty” or “Omniscient, omniscient, omniscient” or “Loving, loving, loving.” They are saying, “Holy, holy, holy.”
What does holiness mean? The word “holiness” comes from the Hebrew word qadas meaning “to separate” or “to cut” (the Greek equivalent of hagios). The idea is that God is separated or cut off from sin and evil; He is a cut above all unrighteousness and a cut above everything He created. Charles Hodge gives this definition in his Systematic Theology:
“Holiness, on the one hand, implies entire freedom from moral evil and, on the other, absolute moral perfection. Freedom from purity is the primary idea of the word. To sanctify is to cleanse; to be holy is to be clean. Infinite purity, even more than infinite knowledge or infinite power, is the object of reverence.” (Systematic Theology, pgs. 150-151)
It means simply that God is without sin and is separated from all evil. He doesn’t see the holy standard and then meet it; He is the standard. God doesn’t need to change, because he is already perfectly holy. He does not do any wrongdoing. God’s holiness means that He is separated from sin and devoted to being the standard of all holiness for all.
This was what Moses was confronted with at the burning bush. When he approached this theophany, the Lord warned him
“Do not draw near this place. Take your sandals off your feet, for the place where you stand is holy ground” (Exod 3:5).
He told Moses, “You are coming to a place void of sin and you are a sinner. Be warned!”
Isaiah had a similar confrontation when he had a vision of God in Isaiah 6. He had a vision of God sitting on his throne surrounded by cherubim, angels and other sentient beings. He saw them saying “Holy, holy, holy” and telling him the entire earth was filled with His glory (Isa 6:3). The foundation shook, smoke filled the room and Isaiah proclaimed,
“Woe is me, for I am undone! Because I am a man of unclean lips, and I dwell in the midst of a people of unclean lips; for my eyes have seen the King, the LORD of hosts” (Isa 6:4).
He was utterly humbled with being in the presence of the holy standard as an unholy man. Men like Moses and Isaiah demonstrate how we are to react to God’s holiness.
When confronted with God’s holiness, some people grow in bitterness; others resent His holiness; some just get enraged; some just trivialize God’s attributes all together. But, the godly reaction to God’s holiness should be thanksgiving and trembling.