Well, this scripture has extra meaning to me, because I work in metallurgy, and we use furnaces to purify steel.
We heat steel up to around 1550 degrees F to purify it, to impregnate it with carbon and other features. I don't actually run the furnaces, so I can't explain exactly what goes on. But the furnaces have to be an exact heat +/- 10 degrees, and the metal must travel through the furnace at a set speed. So it must be heated an exact time.
We then have what is called "quench" which cools the metal instantly. This also removes impurities and creates a "grain", not unlike wood grain. However, the quench makes the steel brittle like glass.
We then super-cool the steel down to minus 120 degrees F. This removes more impurities and again forms the perfect size grain. However, the steel is very brittle now.
Finally we must "temper" the steel which makes it soft and malleable, so that it does not crack. It is no longer brittle. This is done by heating the steel up to from around 350-700 degrees F for a specified time. Everything must be very exact.
So, there are quite a few steps to making good steel that is durable for the purpose intended and will not crack under stress.
What is amazing to me is that this science goes back thousands of years. Steel has to be made in an "atmosphere", or various gases to be made properly. I am amazed they discovered this in the ancient past.
Anyway, enough of that, this scripture tells me the word of God is pure. It does not contain mistakes. It is without error. It is like silver that has been melted down 7 times and all the impurities scrapped off so that it is as pure as it can possibly be.
Now, I have heard theories about the word of God being purified 7 times in English. There might be something to this, or maybe not.
That doesn't matter to me, I believe God has preserved his word by faith, and in English I believe it is the King James Bible.