Priests are an instrument used by God for the salvation of souls
No matter how people make successes and achievements in mundane life, they still miss an important part of their lives, namely the spiritual aspect.
No matter how powerful and influential people become, they are still impotent as they still seek a divine power that guides them in their lives.
When people become sick, they feel hopeless. They restore their hope when they get close to a superpower, namely a divine power that can extricate them from their suffering.