Throughout the Old Testament, Israel built a lot of altars. This is particularly true before the establishment of the Temple, when Israel was looking for ways to mark her history with God in remembrance and worship. And one of the rules for building altars was that you had to use uncut stones; you couldn't shape the altar any old way you wanted to.
And this is true, too, when Moses climbs the mountain to receive the commandments from the Lord. He famously took two stone tablets with him, and when he shattered those tablets in frustration at Israel's sin, he took two more. Most of the time that we see these tablets in modern Christianity, they are beautiful to look at. Curved on the top, usually. Polished. Well-shaped. But the Scriptures tell us that these, too, were uncut stones. They were raw tablets with rough edges and natural shapes.
The principle here is pretty simple: you don't have to worry about making things pretty when God makes them beautiful.
A second principle just as simple: God shapes the holy things, not you.
This is really the essence of it all, and it has to be. We are a people prone to worship beauty, to want things that are carefully crafted and made in just a certain way. And it's not that God doesn't care about these things; He does. You need look no further than the exquisite detail of the Tabernacle and the Temple to see that. He absolutely cares about them.
But He also understands our inclination to worship beautiful things instead of what those beautiful things are meant to draw us to. We might worship the tablets over the Lawgiver, the altar over the remembrance of the Lord. If we make things beautiful, we become more invested in them - in the things. But if we have raw things that the Lord has made beautiful for us, we are most invested in the Lord's beauty and gift.
It goes back to one of the commands inscribed on that stone - you shall not make idols. You shall not labor to make beautiful things that will take your worship away from the Lord, and that includes beautiful things you think will draw you closer to Him. You will not fashion with your own hands anything that would cause you to worship it, that would have you more invested in the thing you made than in the reason you made it.
And we do this all the time, right? It's so easy. Especially as we have gotten away from this command and entered into a culture that loves the beautiful. We sing beautiful songs with the radio, and we think, oh, what a beautiful song; how I love this beautiful song. But we get so busy singing the beautiful song that we don't even connect with the beautiful Lord it is meant to worship. Or we buy fancy new Bibles with beautiful covers and elegant type, and we think, Oh, what a beautiful Bible. And then we take great care not to mark or to mar it in any way, keeping it well-protected from our lives because it is such a beautiful Bible. And that keeps us from messily engaging with the beautiful God revealed in its pages.
We build our churches with beautiful entrances and shining altars and all the latest and the best that technology has to offer us, and then we promote our churches for our programs and services and buildings...and not our God. When was the last time you saw a church say, "Come join us! We love Jesus here!" No, you're far more likely to see, "Convenient service times! Free coffee! Casual dress code! Multimedia available! And here's a picture of our beautiful building!"
That's precisely why God made this rule. It's why He is so insistent about it. When you build things for God, when you make things for the Lord, you make them raw. Natural. Ugly. You let them be whatever they are, you bring them as they come - uncut. You let God make them beautiful, lest they draw your heart away from Him.
There is simply no other way.