Consider a series of transactions for a certain amount of money. Each transaction has a tax cost, that reduces that "certain amount" of money. On average, six transactions return all of that "certain amount" of money back to the treasury/ per Krugman.
Taxes take the money out of circulation, and the government AGAIN spends the money. It is two transactions. This technicality is important. Following where the money goes and the steps that it takes to how it gets there is how you get some understanding of economics. Government bonds are the safe haven in that largely stays even with inflation. That funds the government in a large way. Taxes, to an increasing degree, pay the interest on that debt.
The interest rates set by the government set the interest rates of corporate bond, of the giants to the little consumer rates by risks taken. These, together, fund loans, which fuels America's economic engine. High interest means slowed growth. Low rates spurs growth.