Driving tractor-trailers, We switch gears because we feel the gear is giving out, because there is a hill or curve approaching. We learn that we are to inspect our tractor and trailer before and, after each trip.
In life, our tractor motor is our soul, our body is the tractor. We are driving along the road of life. Some of us are still learning how to switch gears. Many of us don't know when a curve is approaching, nevertheless a hill. Many people inspect their bodies, forget they have a soul.