Mediator : one who intervenes between two persons who are at variance, with a view to reconcile them. This word is not found in the Old Testament; but the idea it expresses is found in Job 9:33, in the word "daysman" (which see), marg., "umpire."
This word is used in the New Testament to denote simply an internuncius, an ambassador, one who acts as a medium of communication between two contracting parties. In this sense Moses is called a mediator in Galatians 3:19.
Christ is the one and only mediator between God and man (1 Timothy 2:5; Hebrews 8:6; 9:15; 12:24). He makes reconciliation between God and man by his all-perfect atoning sacrifice. Such a mediator must be at once divine and human, divine, that his obedience and his sufferings might possess infinite worth, and that he might possess infinite wisdom and knowlege and power to direct all things in the kingdoms of providence and grace which are committed to his hands (Matthew 28:18; John 5:22,25,26,27); and human, that in his work he might represent man, and be capable of rendering obedience to the law and satisfying the claims of justice (Hebrews 2:17,18; 4:15,16), and that in his glorified humanity he might be the head of a glorified Church (Romans 8:29).
This office involves the three functions of prophet, priest, and king, all of which are discharged by Christ both in his estate of humiliation and exaltation. These functions are so inherent in the one office that the quality appertaining to each gives character to every mediatorial act. They are never separated in the exercise of the office of mediator.