The word “mediator” literally means to be in the middle or midst. It is “‘one who mediates’ between two parties with a view to producing peace” (Vine’s Expository Dictionary). Moses was the mediator God used to make the Old Testament covenant of Law between Himself and the Jews. In the New Testament, Jesus is the mediator between God and mankind (1 Timothy 2:5)
Jesus is the New Testament mediator between God and mankind (1 Timothy 2:5). There are some sharp contrasts between the mediation of Jesus in the N.T. and that of Moses in the Old Testament Law. First, Moses was only a man and was therefore limited in his ability to adequately represent God. However, Jesus was uniquely God and man (1 Timothy 3:16); therefore, He was a perfect mediator, knowing by experience both sides of the issue.
Second, Jesus did what Moses could not do. He went beyond mediation to actually become the sacrifice that would satisfy the justice of the one party (God) by bearing the sins of the other party (mankind). When Jesus rose from the dead, He (the mediator) also became the guarantor that His settlement would work. “Wherefore he is able also to save them to the uttermost that come unto God by him, seeing he ever liveth to make intercession for them” (Hebrews 7:25).
What did Paul mean here? A mediator mediates between two parties who are in conflict with each other. Therefore, by using the statement “a mediator is not a mediator of one,” he was saying that mediators don’t settle disputes among themselves–they are the go-between for two other parties.
However, the mediation of Jesus was very unique. Jesus was God and mankind at the same time. Therefore, He was reconciling Himself (His humanity and all His children by faith) to Himself (His divinity; i.e., His Father). This is what Paul referred to when he said, “But God is one.”