Why trust the Bible?

Psalm 12:6 says “The words of the LORD are flawless, like silver refined in a furnace of clay, purified seven times.”
God’s words (the text of the Bible), is like silver refined seven times

Why not just refined once once?

“Seven” in the Bible is the number for completeness and wholeness.  What Psalm 12:6 is saying is that God’s words are completely pure, without error and wholly reliable.

Yet, there may be more to the number seven:

The first refining fire was used to burn away the combustibles in the silver bearing rock.

Then the ore container (the clay pot) was sealed from the air, first having some material added, such as charcoal, which would chemically remove the oxygen from the silver oxide. This would result in silver metal flowing to the bottom of the container with the molten rock (the slag) above it. The process was repeated a few times so that all the reclaimable silver was removed from the valuable ore.

The next problem that had to be solved was to remove the impurities such as copper, arsenic etc. in the silver and because they have different melting temperatures, they had to be carefully removed in fires of different temperatures.

Also, because not much coal or coke was available, wood had to be used and this first had to be converted into charcoal to remove its impurities because any smoke resulting from say the wax or oil in the wood that reached the molten metal would cause further impurities in the metal.

Fluxes, such as beeswax were also discovered, which in certain circumstances formed a film over the surface of the molten metal, also causing impurities to separate and float to the surface.

Further, a blast of air had to be forced through the burning charcoal with the aid of bellows so that the fire would burn hot enough.
We see that the refining of silver was a fairly complex process – seven fires probably had to be used. Further, this process was learned over a period of many generations of metalworkers and silversmiths. If the wrong process was used, the resultant metal could have been copper instead of silver.  If the fire was not hot enough because of the laziness of the silversmith in using the bellows, impure silver would have resulted.
Here’s the bottom line: You can trust the Bible. It’s pure. There’s no errors.  It’s God’s words. 
(Thanks to Derek Prince for the insights.)