In a lecture titled “The Meaning of Holiness” (video), R. C. Sproul identifies two major scriptural meanings to the word holiness, one primary and one secondary, one in relation to God and one in relation to human beings.
The primary meaning is in relation to God, and it refers to his being separate or other. “When the Bible speaks about God’s holiness,” explains Sproul, “the primary thrust of those statements is to refer to God’s transcendance, to refer to his magnificence, to refer to that sense in which God is higher and superior to anything that there is in the creaturely realm.”
This meaning of holiness is implied all throughout the Bible, as it characterizes all of God’s attributes. God is holy in glory (Isaiah 6:3), power (Isaiah 52:10) and righteousness (Isaiah 5:16). For God to be holy means that, unless God makes it so, there is no one and nothing like him in any way.
Your way, O God, is holy. What god is great like our God? (Psalm 77:13)
Who will not fear, O Lord, and glorify your name? For you alone are holy. (Revelation 15:4)
The secondary meaning refers to our righteousness and purity. Holiness is the manner in which, by the Holy Spirit, God’s people live and act as imitators of God’s character, which is separate and other from the manner in which the world around us lives.
As obedient children, do not be conformed to the passions of your former ignorance, but as he who called you is holy, you also be holy in all your conduct, since it is written, “You shall be holy, for I am holy.” (Peter 1:14-16)
Since we have these promises, beloved, let us cleanse ourselves from every defilement of body and spirit, bringing holiness to completion in the fear of God. (2 Corinthians 7:1)