That's not exactly true. Money in the bank is invested and is different than consumption money.
One drive the offer, the second one drive the demand. The economy is basically the flow from one pot to the other.
With interest rate at historical low, large business with trillion hoarded, money is already plentiful on the investment side. This article is just claiming that there is portion of that investment money could be reallocated on the consumption side which would indeed allow the economy to run.
The article is very optimistic that this money is really what is missing. Personally not quite sure about that as the economy already relies on historically high level of debt on the consumer side (i.e. consumer spend today and tomorrow money), adding fresh money in the system is at best a short term "solution", adding memory to a memory leaking system.
The problem is that there is simply not enough money flowing from the investment pot into the consumer pot. i.e. salaries are too low, tax on profit are too low, ... something isn't balanced and we are all playing economic musical chair, with people hoarding money to avoid being without once the system breaks.
