In 1929, real-estate & stock prices plummeted, leaving many borrowers deep in debt. For four years, nobody was borrowing any money -- interest-rates fell from 6% to less than 1%, signaling that banks were offering their loanable cash for lower & lower rates, and still nobody was borrowing. That means money gets "stuck" in the banks & credit-markets, as people (slowly) save into banks, without those monies being re-borrowed, re-spent, and re-circulated. That slowed spending, which didn't rise again, until everybody began borrowing again, from 1934 onwards.
Keynes insight, was for Government to exploit such situations, to borrow all that loanable cash, being passed over by the private sector, as they focused on saving, to pay down their debts. Government could wade into the credit-market, without crowding out private sector borrowers, and gobble up gobs of funds, for low-low interest-rates. Government would be a "borrower of last resort", borrowing, spending, and circulating cash that otherwise would have sat in banks, decirculated, and deflating the money supply. Hypothetically, Government could have borrowed billions of dollars, at low interest rates, to
- buy up farm crops (and ship to soup kitchens in cities)
- buy up farm & house mortgages, eliminating foreclosures, and keeping US citizens off their streets
- pay for rent & utility bills, eliminating evictions, and keeping people off the streets
Those would have been the kinds of focused borrowings that Keynes would have advocated (to my understanding).
Keynes did not advocate the ratchet-effect, whereby Government budgets refuse to reduce.