MV=PT
What you see above is central basis by which to interoperate all of the fed's behavior.
The above equation roughly translates to:
(Money supply) * (Turnover rate) = (Price) * (Transactions)
where: -money supply is outstanding cash or dollars -turn over rate is the frequency in which the cash changes hands = All the transactions that took place and their price
Current dogma of keynesian academic economists is that an ability to control the money supply will affect the rest of the equation and in theory the real economy. So (Money supply) is the variable the fed can control they use to pull the levers of our economy.
What's implied here then is a gross misunderstanding of what money actually is: a means of instrumentation and measurement.
For economies to properly function, entrepreneurs and participants in the economy need a consistent and reliable gauge to measure the performance of their (economic) experiments.
When supply of money in relation to other "things" is constantly and artificially manipulated, it becomes near impossible for the prices of goods and services to reflect actual information about fundamentals, comparative advantages, etc.
If you're technically inclined, I am essentially making an argument from the perspective of information theory.
Claude Shannon basically showed that to convey information, you need a medium that stays constant. Without that, it's impossible to distinguish the "medium" from the "message".
This is precisely what our academic oriented economists in charge of the fed and our prevailing economic school of thought have fucked up: They've tried to send a message through the medium itself in an attempt to activate parts of the economy, and have completely fooled themselves into thinking that while socialism and command economies are bad, control of the money supply is somehow different.
The issue is what people don't realize, is that free markets aren't about free exchanges of goods and services, but about free exchanges of information. And through the temptations and hubris of central planning they've compromised the medium through which participants in the economy can exchange information.