When does a person need a mediator? Have you ever experienced mediating between two parties?
One of the errors taught by the Roman Catholic Church is the doctrine of Mediatrix—the belief that Mary the mother of Jesus on earth can mediate for us in heaven. Thus Roman Catholics invoke her help by praying the rosary and reciting the "Hail Mary" prayer several times. They also solicit the help of other saints like St. Peter as well as their local patron saints.
In other religions, especially pagan religions, the praying individuals seek the assistance of their dead ancestors. They believe that their dead loved ones are not really dead, but exist in another world and can help them in their dilemma.