To be holy is to be set apart for God, and to become like the God you are set apart for. Holiness starts not with a rule list but with God's own character: He says, 'You shall be holy; for I, Yahweh your God, am holy,' and then sets His people apart from the world so that their lives look like Him.
Not a summary of these passages: the passages themselves. Read them, then come back to the study below.
The study
What the Scripture says
1
Holiness means set apart before it means moral perfection
The root idea of holiness is separation for a purpose: 'have set you apart from the peoples, that you should be mine.' Israel was holy the way temple vessels were holy: reserved for God's use. That status came first by God's act, and only then demanded a corresponding life.
You shall be holy to me; for I, Yahweh, am holy, and have set you apart from the peoples, that you should be mine.And ye shall be holy unto me: for I the Lord am holy, and have severed you from other people, that ye should be mine.
and you shall be to me a kingdom of priests, and a holy nation.’ These are the words which you shall speak to the children of Israel.”And ye shall be unto me a kingdom of priests, and an holy nation. These are the words which thou shalt speak unto the children of Israel.
The command comes with its reason attached: 'You shall be holy; for I, Yahweh your God, am holy.' Scripture calls God 'the high and lofty One who inhabits eternity, whose name is Holy' and heaven rings with 'Holy, holy, holy.' Holiness is not one attribute among many; it is the purity and otherness of everything God is.
“Speak to all the congregation of the children of Israel, and tell them, ‘You shall be holy; for I, Yahweh your God, am holy.Speak unto all the congregation of the children of Israel, and say unto them, Ye shall be holy: for I the Lord your God am holy.
For thus says the high and lofty One who inhabits eternity, whose name is Holy: “I dwell in the high and holy place, with him also who is of a contrite and humble spirit, to revive the spirit of the humble, and to revive the heart of the contrite.For thus saith the high and lofty One that inhabiteth eternity, whose name is Holy; I dwell in the high and holy place, with him also that is of a contrite and humble spirit, to revive the spirit of the humble, and to revive the heart of the contrite ones.
One called to another, and said, “Holy, holy, holy, is Yahweh of Armies! The whole earth is full of his glory!”And one cried unto another, and said, Holy, holy, holy, is the Lord of hosts: the whole earth is full of his glory.
In the Old Testament, holiness touched ordinary life
Leviticus 19 puts 'be holy' next to leaving harvest gleanings for the poor, paying workers on time, just measures, and loving your neighbor as yourself. Being set apart was never mainly ritual; it showed in how God's people treated people. A holy nation looked different because it did justice and mercy in a world that didn't.
“Speak to all the congregation of the children of Israel, and tell them, ‘You shall be holy; for I, Yahweh your God, am holy.Speak unto all the congregation of the children of Israel, and say unto them, Ye shall be holy: for I the Lord your God am holy.
“‘When you reap the harvest of your land, you shall not wholly reap the corners of your field, neither shall you gather the gleanings of your harvest. You shall not glean your vineyard, neither shall you gather the fallen grapes of your vineyard; you shall leave them for the poor and for the foreigner. I am Yahweh your God. “‘You shall not steal. “‘You shall not lie. “‘You shall not deceive one another. “‘You shall not swear by my name falsely, and profane the name of your God. I am Yahweh. “‘You shall not oppress your neighbor, nor rob him. “‘The wages of a hired servant shall not remain with you all night until the morning. “‘You shall not curse the deaf, nor put a stumbling block before the blind; but you shall fear your God. I am Yahweh. “‘You shall do no injustice in judgment. You shall not be partial to the poor, nor show favoritism to the great; but you shall judge your neighbor in righteousness. “‘You shall not go up and down as a slanderer among your people. “‘You shall not endanger the life of your neighbor. I am Yahweh. “‘You shall not hate your brother in your heart. You shall surely rebuke your neighbor, and not bear sin because of him. “‘You shall not take vengeance, nor bear any grudge against the children of your people; but you shall love your neighbor as yourself. I am Yahweh.And when ye reap the harvest of your land, thou shalt not wholly reap the corners of thy field, neither shalt thou gather the gleanings of thy harvest. And thou shalt not glean thy vineyard, neither shalt thou gather every grape of thy vineyard; thou shalt leave them for the poor and stranger: I am the Lord your God. Ye shall not steal, neither deal falsely, neither lie one to another. And ye shall not swear by my name falsely, neither shalt thou profane the name of thy God: I am the Lord. Thou shalt not defraud thy neighbour, neither rob him: the wages of him that is hired shall not abide with thee all night until the morning. Thou shalt not curse the deaf, nor put a stumblingblock before the blind, but shalt fear thy God: I am the Lord. Ye shall do no unrighteousness in judgment: thou shalt not respect the person of the poor, nor honour the person of the mighty: but in righteousness shalt thou judge thy neighbour. Thou shalt not go up and down as a talebearer among thy people: neither shalt thou stand against the blood of thy neighbour: I am the Lord. Thou shalt not hate thy brother in thine heart: thou shalt in any wise rebuke thy neighbour, and not suffer sin upon him. Thou shalt not avenge, nor bear any grudge against the children of thy people, but thou shalt love thy neighbour as thyself: I am the Lord.
“‘You shall do no unrighteousness in judgment, in measures of length, of weight, or of quantity. You shall have just balances, just weights, a just ephah, and a just hin. I am Yahweh your God, who brought you out of the land of Egypt.Ye shall do no unrighteousness in judgment, in meteyard, in weight, or in measure. Just balances, just weights, a just ephah, and a just hin, shall ye have: I am the Lord your God, which brought you out of the land of Egypt.
and you shall be to me a kingdom of priests, and a holy nation.’ These are the words which you shall speak to the children of Israel.”And ye shall be unto me a kingdom of priests, and an holy nation. These are the words which thou shalt speak unto the children of Israel.
When Isaiah saw the Lord high and lifted up, his first words were about himself: 'Woe is me! For I am undone.' That is how holiness works: God's purity exposes our uncleanness, but it does not leave us there. The burning coal touched Isaiah's mouth, his guilt was taken away, and only then did he hear the call to go.
One called to another, and said, “Holy, holy, holy, is Yahweh of Armies! The whole earth is full of his glory!”And one cried unto another, and said, Holy, holy, holy, is the Lord of hosts: the whole earth is full of his glory.
Then I said, “Woe is me! For I am undone, because I am a man of unclean lips, and I dwell in the midst of a people of unclean lips: for my eyes have seen the King, Yahweh of Armies!” Then one of the seraphim flew to me, having a live coal in his hand, which he had taken with the tongs from off the altar. He touched my mouth with it, and said, “Behold, this has touched your lips; and your iniquity is taken away, and your sin forgiven.” I heard the Lord’s voice, saying, “Whom shall I send, and who will go for us?” Then I said, “Here I am. Send me!”Then said I, Woe is me! for I am undone; because I am a man of unclean lips, and I dwell in the midst of a people of unclean lips: for mine eyes have seen the King, the Lord of hosts. Then flew one of the seraphims unto me, having a live coal in his hand, which he had taken with the tongs from off the altar: And he laid it upon my mouth, and said, Lo, this hath touched thy lips; and thine iniquity is taken away, and thy sin purged. Also I heard the voice of the Lord, saying, Whom shall I send, and who will go for us? Then said I, Here am I; send me.
For Christians, holiness is calling, choice, and destination
Peter quotes Leviticus to the church: 'you yourselves also be holy in all of your behavior.' Paul urges believers to present their bodies 'a living sacrifice, holy, acceptable to God.' And we were chosen in Christ 'that we would be holy and without defect before him.' Holiness is pursued now, and completed then; Hebrews calls it the sanctification 'without which no man will see the Lord.'
but just as he who called you is holy, you yourselves also be holy in all of your behavior; because it is written, “You shall be holy; for I am holy.”But as he which hath called you is holy, so be ye holy in all manner of conversation; Because it is written, Be ye holy; for I am holy.
Therefore I urge you, brothers, by the mercies of God, to present your bodies a living sacrifice, holy, acceptable to God, which is your spiritual service.I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service.
even as he chose us in him before the foundation of the world, that we would be holy and without defect before him in love;According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love:
Follow after peace with all men, and the sanctification without which no man will see the Lord,Follow peace with all men, and holiness, without which no man shall see the Lord:
“Speak to all the congregation of the children of Israel, and tell them, ‘You shall be holy; for I, Yahweh your God, am holy.Speak unto all the congregation of the children of Israel, and say unto them, Ye shall be holy: for I the Lord your God am holy.
One called to another, and said, “Holy, holy, holy, is Yahweh of Armies! The whole earth is full of his glory!”And one cried unto another, and said, Holy, holy, holy, is the Lord of hosts: the whole earth is full of his glory.
but just as he who called you is holy, you yourselves also be holy in all of your behavior; because it is written, “You shall be holy; for I am holy.”But as he which hath called you is holy, so be ye holy in all manner of conversation; Because it is written, Be ye holy; for I am holy.
Therefore I urge you, brothers, by the mercies of God, to present your bodies a living sacrifice, holy, acceptable to God, which is your spiritual service.I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service.
even as he chose us in him before the foundation of the world, that we would be holy and without defect before him in love;According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love: