Holiness refers primarily to the quality of God, denoting his transcendent apartness from the rest of creation, his uniqueness, and his total purity. When the term is applied to people, things, or places that have been touched by the presence of God or dedicated to God, it connotes the idea of being set apart for God and thus belonging to the realm of the divine, which is morally and ceremonially pure.

The biblical concept of “holiness” is grounded in the idea of being set apart and transcendently distinctive. When the Bible claims that God is holy, it means primarily that he is radically distinctive in sphere, in character, and in requirements. He is high above human beings (1 Sam 2:2) and distinctive from all other deities (Exod 15:11; Pss 86:8–10; 99:2–3). As a quality or attribute of God, the term also carries the sense of “morally good” and “ethically pure.” Thus, the holiness of God entails that God’s character is totally good and entirely without evil (Hab 1:13). The triple repetition of “holy” in Isaiah 6:3 expresses that God’s holiness is superlative and embrace the entirety of his divine nature. The term can be applied to persons, things, places, or times that are touched by or devoted to God. Since God is holy, whatever comes into contact with God or his presence is immediately holy and thus belongs to the realm of the sacred. In Exodus 3:5, God’s presence makes the ground on which Moses stands holy.

The New Testament concept of holiness is partially informed by the overlap with the Old Testament concept of being set apart and sacred. The Septuagint primarily renders the concept of distinctiveness and being devoted or belonging to God with the family of Greek words that includes ἅγιος (hagios, “holy”). Other words such as ὅσιος (hosios, “devout”) are also employed to convey the nuances of holiness. The concept is contrasted with the ideas of being common, profane, impure and defiled.

In both the Old Testament and New Testament, holiness is presented as a calling and a command to the people of God. Holiness itself or the desire for holiness is often presented as the prime characteristic and standard of behavior for worshippers (Lev 11:44–45) and Christians, patterned after the reality of God’s innate holiness (Lev 19:2; 1 Pet 1:16). In the nt, Christians are addressed by the term “the holy ones” or “the saints” (hagios; Phil 1:1, Eph 1:1, Heb 3:1), indicating that they are a group of people called by God and set apart for divine purposes.

Source: Hon Lee Kwok, “Holiness,” in Mangum, Douglas, Derek R. Brown, Rachel Klippenstein, and Rebekah Hurst, eds. Lexham Theological Wordbook. Lexham Bible Reference Series. Bellingham, WA: Lexham Press, 2014.