The slope of the yield curve is potentially informative for several reasons. To some extent, it captures the stance of monetary policy. For example, when the yield curve is sharply upward sloping, as is the case today, one can usually conclude that monetary policy is in an expansionary mode (because the short-term policy rate lies below the average of expected future short-term rates).
Either an expected pickup in economic growth or higher expected future inflation would also tend to raise long-term rates relative to short rates, steepening the yield curve.