The saving ministry of Jesus Christ is summed up in the statement that He is the "Mediator between God and men" (1 Tim 2:5). A mediator is one who brings together parties who are out of communication and who may be alienated, estranged, or at war with each other. The mediator must have links with both sides so as to identify with and maintain the interests of both, and represent each to the other on a basis of goodwill. Thus Moses was mediator between God and Israel (Gal. 3:19), speaking to Israel on God's behalf when God gave the law (Ex. 20:18-21) and speaking to God on Israel's behalf when Israel had sinned (Ex. 32:9-33:17).
Every member of our fallen and rebellious race is by nature in "enemity against God" (Rom 8:7), standing under God's wrath, the punitive rejection whereby as Judge He espresses active anger at our sins (Rom 1:18; 2:5-9; 3:5, 6). Reconcilliation of the alienated parties is needed, but can only occur if God's wrath is quenched and the human heart, that opposes God and motivates a life against God, is changed. In mercy, God sent His Son into the world to bring about the needed reconciliation. It was not that he kindly Son acted to placate the harsh Father; the initiative was the Father's own. In Augustine's words, "in a wonderful and divine way even when He hated us, he loved us" (Commentary on John 110.6; cf. John 3:16; Rom. 5:5-8; 1 John 4:8-10). In all His mediatorial ministry the Son was doing His Father's will (see "The humble Obedience of Christ" at John 5:19).
Objectively and once for all, Christ achieved reconciliation for His people through penal substitution. On the cross He took our place, carried our identity as it were, bore the curse due to us (Gal. 3:13), and by His sacrificial shedding of blood made peace for us (Eph. 2: 16-18; Col. 1:20). Peace here means an end to hostility, guilt, and exposure to the retributive punishment that was otherwise unavoidable - in other words, forgiveness for all the past, and eternal, personal acceptance for the future. Those whio have received reconcilitation through faith in Christ are justified and have peace with God (Rom. 5:1, 10). The Mediator's present work, which He carries forward through human messengers, is to persuade those for whom He achieved reconciliation actually to receive it (John 12:32; Rom. 15: 18; 2 Cor. 5:18-21; Eph. 2:17).
Jesus is "the Mediator of the new covenant" (Heb. 9:15; 12:24), the initiator of a new relationship of conscious peace with God, going beyond what was known under the Old Testament arrangements for dealing with the guilt of sin (Heb. 9:11-10:18).
One of Calvin's great contributions to Christian understanding was his observation that the New Testament writers expound Jesus' mediatorial ministry in terms of the three "offices" (defined roles) of prophet, priest, and king. These three aspects of Christ's work are found together in the letter to the Hebrews, where Jesus is both the messianic King, exalted to His throne (1:3, 13; 4:16; 2:9), as well as the great High Priest (2:17' 4:14 - 5:10 chs. 7:10), who offered Himself to God as a sacrifice for our sins. In addition, Christ is the massage concerning Himself (2:3). In Acts 3:22 Jesus is called a "Prophet" for the same reason that Hebres calls Him "Apostle," namely, because He instructed people by declaring to them the word of God.
While in the Old Testament the mediating roles of prophet, priest, and king were fulfilled by separate individuals, all three offices now coalesce in the one person of Jesus. It is His glory, given Him by the Father, to be in this way the all-sufficient Saviour. We who believe are called to understand this, and to show ourselves His people by obeying Him as our king, trusting Him as our priest, and learning from Him as our prophet and teacher. To center on Jesus Christ in this way is the hallmark of authentic Christianity.