One major reason for this emphasis is the recognition that the stance of monetary policy encompasses not just the current level of the short-term policy rate but its expected future path as well. Economists have come to understand that expectations about monetary policy can play an important role in determining economic outcomes, such as real economic growth and inflation.
For example, today’s decision to save or to spend is influenced by the current interest rate as well as tomorrow’s expected future consumption. In turn, tomorrow’s expected future consumption is influenced by next period’s interest rate and next period’s expected future consumption. Therefore, the entire expected path of interest rates, not just the current interest rate, influences today’s consumption.