In principle, there are only three main components of spending that much matter to monetary policy: consumer spending, business investment and exports and trade.

The remark frames monetary policy as operating mainly through the demand side of the economy. By singling out consumer spending and business investment, it points to the classic interest-rate transmission mechanism: tighter policy tends to discourage borrowing and spending, while looser policy encourages it. Adding “exports and trade” highlights the exchange-rate channel: rate changes can affect currency values and thus net exports. The phrasing “in principle” suggests a simplifying, pedagogical intent—reducing a complex macroeconomic picture to a few levers that central banks can plausibly influence—while implicitly downplaying other components (notably government spending) as less directly responsive to central-bank decisions.