The Hebrew qodesh is the central word for holiness, sacredness, consecration, and the sanctuary (the holy place). It derives from a root meaning 'to cut' or 'to separate' — something holy is set apart from the common and ordinary for God's exclusive use and presence.
Qodesh is the cornerstone of Old Testament theology. God's fundamental nature is holiness (Isaiah 6:3 — 'Holy, holy, holy is the LORD Almighty') and His primary demand of His people is holiness: 'Be holy (qadosh) because I, the LORD your God, am holy' (Leviticus 19:2). The entire Levitical system — the tabernacle, priesthood, sacrifices, calendar — is a structured meditation on holiness and how sinful humans can approach the Holy God. Qodesh thus encompasses both God's awesome, dangerous 'otherness' and the invitation to share in that otherness through consecration. The New Testament identifies believers as 'hagios' (holy ones, saints) — called out of the world, set apart for God, progressively transformed into the holy character of Christ (Romans 12:1–2; 1 Peter 1:15–16).