The threefold office (Latin: munus triplex) of Jesus Christ is a Christian doctrine based upon the teachings of the Old Testament of which Christians hold different views. It was described by Eusebius and more fully developed by John Calvin.
In the Old Testament, the appointment of someone to any of these three positions could be sanctioned by anointing him by pouring oil over his head. Thus the term messiah, meaning "anointed one", is associated with the concept of the threefold office. While the office of king is that most frequently with the Messiah, the role of Jesus as priest, which involves intercession before God, is also prominent in the New Testament, being most fully explained in chapters 7 to 10 of the Book of Hebrews.
Eusebius worked out this threefold classification, writing: "And we have been told also that certain of the prophets themselves became, by the act of anointing, Christs in type, so that all these have reference to the true Christ, the divinely inspired and heavenly Word, who is the only high priest of all, and the only King of every creature, and the Father's only supreme prophet of prophets." During the Reformation this concept played a substantial role in scholastic Lutheran Christology and in the christology of Reformed theologians such as John Calvin as well as that of John Wesley.
Christ is the mouthpiece of God as the Prophet, speaking and teaching the Word of God, infinitely greater than all prophets, who spoke for God and interpreted the will of God. The Old Testament prophet brought God's message to the people. Christ, as the Word (John 1:1-18)/Logos is the Source of revelation. Accordingly, Jesus Christ never used the messenger formula, which linked the prophet's words to God in the prophetic phrase, Thus says the Lord. Christ, being of the same nature, provides a definitive and true exposition of God.
The Word/Logos is Light. As the true Light (John 1:1-18), Jesus Christ exclusively enlightens humankind in the office of Prophet. Jesus affirmed his Divine identity and ultimate authority, revealing God to humanity, continuing His work into the future as the Light (Revelation 22:3).
Christ, whom believers draw near to in confidence, offered Himself as the sacrifice for humanity as High Priest (Hebrews 4:14). Old Testament priests declared the will of God, gave the covenant of blessing, and directed the processing of sacrifices. The priest represented humankind before God. While humankind took the office of priesthood in their weakness, Jesus holds the position with an indestructible power that overcomes the weakness of humanity as described throughout the book of Hebrews. As High Priest, Christ became one with humanity in human weakness, offered prayers to God, chose obedience through suffering, and sympathized with the struggles of humanity.
The atoning death of Christ is at the heart of His work as High Priest. Metaphors are used to describe His death on the cross, such as, "Christ, the Lamb of God, shed His blood on the cross as the sin offering for humankind." Christ made one sin offering as High Priest in contrast to the Old Testament priests, who continually offered sacrifices on behalf of humanity. Because of the work of Christ on the cross, humanity has the opportunity to have a living relationship with God. Conversely, the individuals that deny the work of God are described as dead in sin, without God and without hope. In traditional Christianity (the Roman Catholic, Eastern Orthodox, Anglican Church, Oriental Orthodox, and Assyrian Churches), it is believed that a priest, having received the Sacrament of Holy Orders through the laying on of hands, shares the one priesthood of Christ, and thus it is only priests who can offer the Eucharistic Sacrifice.
Christ, exalted High Priest, mediates the sin that estranges humankind from the fellowship of God. In turn, He has full rights to reign over the church and world as King. Christ sits at the right hand of God, crowned in glory as "King of kings and Lord of lords". "God put this power to work in Christ when he raised him from the dead and seated him at his right hand in the heavenly places, far above all rule and authority and power and dominion, and above every name that is named, not only in this age but also in the age to come. And he has put all things under his feet and has made him the head over all things for the church."
Q. Why is he called "Christ," meaning "anointed"?
A. Because he has been ordained by God the Father
The Westminster Shorter Catechism explains the role of Christ as redeemer in terms of the threefold office:
Q. 23: What offices doth Christ execute as our Redeemer?
Q. 24: How doth Christ execute the office of a prophet?
Q. 25: How doth Christ execute the office of a priest?
Q.26: How doth Christ execute the office of a king?
(a) The prophetical office (munus, or officium propheticum) includes teaching and the miracles of Christ.
(b) The priestly office (munus sacerdotale) consists of the satisfaction made for the sins of the world by the death on the cross, and in the continued intercession of the exalted Savior for his people (redemptio et intercessio sacerdotalis).
(c) The kingly office (munus regium), whereby Christ founded his kingdom, defends his church against all enemies, and rules all things in heaven and on earth. The old divines distinguish between the reign of nature (regnum naturae sive potentiae), which embraces all things; the reign of grace (regnum gratiae), which relates to the church militant on earth; and the reign of glory (regnum gloriae), which belongs to the church triumphant in heaven.
The theologians who followed Luther and Melanchthon down to the middle of the seventeenth century treat Christ's saving work under the two heads of king and priest. Calvin, in the first edition of his Institutes of the Christian Religion (1536), did the same, and it was not till the third edition (1559) and the Genevan Catechism that he fully presented the three offices. This convenient threefold division of the office of Christ was used by the theologians of both confessions during the seventeenth century. Ernesti opposed it, but Schleiermacher restored it.
In his 5th century Gospel harmony book Harmony of the Gospels Saint Augustine viewed the variations in the gospel accounts in terms of the different focuses of the authors on Jesus: Matthew on royalty, Mark on humanity, Luke on priesthood and John on divinity.