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Holiness
In plain words
Holiness means being set apart for God: pure, different and fully His.
In the Bible, holy first describes God. He is completely pure, good and unlike anything else. When the prophet Isaiah saw a vision of God, angels kept calling "Holy, holy, holy" (Isaiah 6:3). Holiness is God's otherness and His goodness together.
For people, holy means set apart for God. Think of a cup kept only for a special occasion. It is not better clay, but it belongs to something special. God calls His people holy because they belong to Him, and then He helps them live like it.
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Peter writes: "Be holy, because I am holy" (1 Peter 1:15-16). This is not a call to be stiff or strange. It is a call to be like God in love, truth and purity. Holiness touches your words, money, sexuality, screens and how you treat people you find difficult.
Many think holiness means a list of things you avoid. It includes that, but it is mainly about who you belong to. Hebrews says to pursue it (Hebrews 12:14), which means real effort. But the effort grows out of grace. You are holy in Christ, so you learn to live holy.
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The Hebrew qadosh and the Greek hagios both carry the sense of separation for God. In the Old Testament, places, objects, days and people were made holy for worship. The prophets pressed that holiness must reach the heart and how you treat the poor, not only temple rituals.
In the New Testament the holy place moves into people: the church and each believer become God's temple by the Spirit. Christians differ in how they express holiness, from simple lifestyle rules to a focus on inner attitude, but they agree it is God's gift and His call to every believer.
My verses
But just as He who called you is holy, so be holy in all you do, for it is written: “Be holy, because I am holy.”
And they were calling out to one another: “Holy, holy, holy is the LORD of Hosts; all the earth is full of His glory.”
Pursue peace with everyone, as well as holiness, without which no one will see the Lord.