One altar, and the cross it points to
The Altar of Unhewn Stone
In the earliest laws given at Sinai, tucked just after the Ten Commandments, God gives instruction about the altars his people are to build. If they make an altar of stone, Exodus 20:25 says, they are not to build it of hewn stone, for lifting a tool upon it pollutes it. The altar was to be of rough, unshaped stones, untouched by the iron of the mason. This page considers that strange and striking command. Why would God refuse the marks of the chisel on the place of sacrifice? The plain instruction is about how Israel was to worship in its first days, before the tabernacle and temple. But the command has drawn out a long reflection in the church about worship that rests on grace rather than human skill, on what God provides rather than what we shape. We will hold the stated and the drawn-out apart with care.
“And if thou wilt make me an altar of stone, thou shalt not build it of hewn stone: for if thou lift up thy tool upon it, thou hast polluted it.”Exodus 20:25
The altar in Scripture
Exodus 20 gives the Ten Commandments, and immediately after them, in the section sometimes called the Book of the Covenant, God adds instructions about worship. He speaks first of an altar of earth on which the people may offer their burnt and peace offerings, promising that in every place where he records his name he will come and bless them. This is the setting: a simple, portable form of worship for a people newly delivered and not yet settled. Then comes the instruction about stone. Exodus 20:25 says that if they build an altar of stone, they are not to build it of hewn or cut stone, because if they lift a tool upon it they have polluted it. The word for the tool refers to the iron implement of the mason. The very act of shaping the stone with a chisel would render the altar unfit. God wanted the stones as they were, rough and natural, not dressed and squared by human craft. The following verse adds a further restriction, that the people are not to go up to the altar by steps, so that their nakedness is not exposed upon it. This concern for modesty and reverence sits alongside the concern about tools. Together the two instructions guard the altar from anything that would dishonor it, whether the pride of ornamentation or the immodesty of exposure. The altar was to be humble in form and approached with reverence. This principle reappears later in Israel's history. When the people entered the land, Joshua built an altar on Mount Ebal of whole, unhewn stones, over which no one had lifted an iron tool, exactly as commanded here and in Deuteronomy. The instruction was not a passing whim but a lasting pattern for how the altar was to be made. The rough stone altar stood in deliberate contrast to the carved and ornamented altars of the surrounding nations, whose worship God's people were to reject.
What it comes to mean
The plainly stated meaning of Exodus 20:25 concerns the making of the altar. God commands that stone altars be built of natural, unhewn stone, and that lifting an iron tool upon them pollutes them. In its immediate context, this likely served several purposes. It kept Israel's worship distinct from the ornate carved altars of the surrounding pagan cultures. It guarded against the temptation to turn the altar itself into a work of art to be admired, drawing glory to the craftsman rather than to God. And it kept worship simple and accessible, buildable by anyone with the stones at hand. The concern about tools may also relate to the association of iron implements with warfare and human violence, kept away from the place where peace with God was sought. Whatever the precise reason, the stated point is clear enough: the altar was not to bear the marks of human shaping. Its unworked roughness was part of its holiness. What made it fit for God was precisely that human craft had not improved it. Here we must be careful to distinguish the stated command from the drawn-out application, because the most familiar use of this verse belongs to the latter. Many preachers and writers have read the unhewn altar as a picture of grace: that our approach to God cannot be improved by the tools of human effort, that every stroke of self-made righteousness only pollutes the place of meeting, and that we come to God on the basis of what he provides rather than what we shape. This is a rich and edifying reflection, and it is not foreign to the wider teaching of Scripture. But Exodus 20 does not itself state this application. It gives a command about stone; the application about works and grace is drawn out by later reflection, and honesty requires us to name it as such. With that distinction kept clear, the drawn-out reflection is worth holding. The instinct to dress the altar, to add our contribution, to leave the mark of our own hand on the place of worship, is deep in us. The command to leave the stone rough confronts that instinct at least in form. It teaches, in its picture if not in its stated words, that there is a worship God receives precisely because we have not tried to make it worthy by our craft.
How it points to Christ, our altar and offering
The New Testament speaks of a temple not made with hands and of living stones built into a spiritual house. In this light the unhewn altar takes on a drawn-out resonance, which we name as reflection rather than as the claim of Exodus. The place where God meets his people is not finally something human skill constructs. It is provided. And the fullest provision is Christ himself, the altar, the priest, and the offering, upon whom no improving hand of human merit can be laid without polluting the very approach he has opened. The gospel presses the point the rough stone only pictures. Our righteousness, Isaiah says, is as filthy rags, and every attempt to dress the altar of our standing before God with the iron tool of self-effort defiles rather than adorns it. Salvation is not partly God's provision and partly our craftsmanship. Ephesians 2 says it is by grace through faith, not of works, lest anyone should boast. The unhewn altar, read through the cross, becomes an image of a salvation we receive rather than shape. So the believer comes to God empty-handed, bringing no tool, adding no stroke. Christ has built the meeting place; we do not improve it. The rough stones of Sinai, whatever their first purpose, gather up into this gospel truth: that at the altar which is Christ, the only fitness is the fitness he provides, and the only pollution is the proud attempt to add our own. We come, as the old hymn says, with nothing in our hands.
Questions people ask
Does Exodus 20:25 actually teach salvation by grace rather than works?
Not in its stated words. The verse gives a command about building altars from natural, unhewn stone rather than cut stone. The application to grace versus human effort is a drawn-out reflection, widely used and consonant with the wider teaching of Scripture, but it is interpretation layered onto the text through the gospel, not something Exodus 20 itself asserts. Honesty means holding the picture and the doctrine together while naming which is which.
Why would using a tool on the stone pollute the altar?
The text does not fully explain, but several reasons fit the context. It kept Israel's worship distinct from the ornate carved altars of pagan nations. It guarded against turning the altar into a work of art that drew glory to the craftsman. Iron tools were also associated with warfare, kept away from the place of peace with God. The rough stone kept worship humble and God-centered.