Money is a metaphor. It stands for the value of all the stuff in the world. There has to be enough money to equate with the value of stuff. When more stuff is made, more money has to be created in order to represent the value of the stuff being made.
If you use a physical thing as your metaphor for value, then, as @HungryGuy said, there is a finite amount of your value metaphor and a constantly growing about of valuable stuff. Thus the money becomes more and more valuable relative to stuff, and you get deflation which destroys an economy.
We don’t need anything to be a metaphor for value. Most transactions don’t just money any more. The vast majority of trading uses electrons. Trying to switch back to the gold standard would crush the economy instantly. A huge depression would occur as transactions become impossibly slow.
An efficient economy needs lightning-fast transactions. Gold is simply too ponderous and stupid to work as currency any more. Even as a standard for currency, it is inflexible, inefficient and just plan bad, overall.
The people who advocate a gold standard have no clue what they are talking about. Fortunately, we would never go back to it because there are too many knowledgeable people in the world. What amazes me is that this idea is still floating around and that anyone pays attention to it at all. Then again, there are still some flat-earthers around, aren’t there?