Jesus the Mediator
A mediator is a person who comes between two people to help them overcome a break in their relationship.
In our daily lives we see mediators used mostly in the legal system. An example would be a person who contracted with the owner of a company to prepare a big party for a wedding. Sometime later the owner of the organization notified the person that they wouldn't be able to provide everything they had promised. The contract between them has been broken; their working relationship is broken. If they cannot mediate between themselves they need a mediator who can find a way to heal the relationship.
The situation between these two people is the same as our relationship with God. Romans 3:23 says "Because all of them have sinned and are deprived of the glory of God." Because of sin, the relationship of each of us with God is broken and its all our fault. God cannot change but we are powerless to do anything to make ourselves acceptable to him. We had nothing to give to pay the debt we owed. Therefore a mediator was required but neither we nor God could act as mediator. Neither can another man or even an angel act as mediator.
The mediator needed to be both God and man and that's what Jesus was. By his death he paid the debt or ransom we owed and by our faith in him we are made righteous before God. That's how Jesus, the mediator, healed the break in the relationship.
1 Timothy 2:5 says "For God is one, and the mediator of God and the sons of men is one: the son of man, Jesus the Messiah, 6 who gave himself a ransom in the place of every person, ..."