The writers of the Old Testament used the word holy over eight hundred times. In the Old Testament, the word group most often referenced to the word holy or holiness is the verb קָדַשׁ, (qadash) to be holy, removed from common use. The standard interpretation of this verb is the idea of separation. This concept has developed over a period of many hundreds, if not, thousands of years. A thorough understanding of this concept is paramount in determining the original intent of the Old Testament authors.
A use frequency in excess of eight hundred provides a broad range of usage and entails numerous nuances. The most common similarities are the idea of separation. The full spectrum includes separation of evil from good, common to a holy use, and the foundational nature of holiness. Because of the importance of this term a survey of its many uses and forms will follow.
The verb qādaš, found eleven times in the Old Testament, in the Qal connotes the state of that which belongs to the sphere of the sacred. When the verb occurs in the Piel and Hiphil stems, it represents the activity used to set apart a person or object from common to sacred use. One use of the Piel stem is when God set apart the Sabbath for his purposes (Genesis 2:3; Exodus 31:13). The Hiphil stem occurs when God commands the Israelites to set apart the firstborn of the men and the animals (Numbers 8:17). These two uses of the verb קָדַשׁ, illustrate the action that separates a person or object from common use to sacred use.
This Qadash word group also have several other forms that will further assist in understanding the idea of holy as proposed by the Old Testament writers. One cognate word is מִקְדָּשׁ (sanctuary), found 74 times in the Old Testament and is used to refer to the tabernacle and the temple, both being places set apart for worship.
Second, the term קָדוֹשׁ (holy) occurs 116 times in the Old Testament and designates that which is intrinsically sacred or is part of the sacred by a divine act. This form of the verb exists in connection with people, things, and even water (Deuteronomy 14:2; Exodus 29:31; Numbers 5:17). When this form appears in connection with God, it projects the significance of a divine scale. Isaiah used this form in his title, The Holy One of Israel. Isaiah used this term twenty-five times and contrasted the evil of Israel to the moral perfection of God and God’s separation from sin (Isaiah 17:7; 30:11). Isaiah also used this in his vision of the throne of God to speak of God’s transcendence and moral holiness. Louis Berkhof refers to God’s transcendent holiness as his majesty-holiness and describes this as God’s absolute distinction from all His creatures.
A second aspect when קָדוֹשׁ exists in the Hebrew text with reference to God, refers to his transcendence, and moral purity. Isaiah’s reaction to his vision properly reflects both the transcendence and purity of God. Isaiah cried out, “Woe is me, for I am ruined! Because I am a man of unclean lips, and I live among a people of unclean lips; for my eyes have seen the King, the Lord of hosts” (Isaiah 6:5).
The final form is the noun קֹדֶשׁ, (holiness) found over four hundred times in the Old Testament. Once again, the idea of separation appears. This separation occurs in reference to the Sabbath and the separation of this holy day from the other days of the week (Exodus 16:23-26; Isaiah 58:13-14). McCabe states, “Whatever the holy God set apart as קֹדֶשׁ is separated from everyday use and consecrated for his holy purpose.”
 Ernst Jenni and Claus Westermann, eds., Theological Lexicon of the Old Testament, vol. 2, trans. Mark D. Biddle (Peabody, MA: Hendrickson Publishers, 1997), p. 1107.
 Robert V. McCabe, “The Old Testament Foundation for Separation” Detroit Baptist Seminary Journal 7 (2002): p. 5.
 John Randolph Jaeggli, “A Historical-Theological Analysis of the Holy One of Israel in Isaiah Forty through Sixty-Six” (Ph.D. dissertation, Bob Jones University, 1987), pp. 40–41.
 Thomas E. McComiskey, “1990 קָדַשׁ,” ed. R. Laird Harris, Gleason L. Archer Jr., and Bruce K. Waltke, Theological Wordbook of the Old Testament (Chicago: Moody Press, 1999), p. 786.
 Unless otherwise indicated, all Scripture is from the English Standard Version Bible (Crossway Bibles, Copyright © 2001, 2007, 2008).
 McComiskey, p. 786.
 John M. Frame, The Doctrine of God (Phillipsburg, NJ: Presbyterian & Reformed, 2002), p. 28.
 Louis Berkhof, Systematic Theology (Grand Rapids, MI: William B. Eerdmans Publishing Company, 1996), p. 73; see also Millard J. Erickson, Christian Theology, 2nd ed. (Grand Rapids: Baker, 1998), p. 311.
 McCabe, p. 9.