In 1215 A.D., one of humanity's great charters of liberty—the Magna Carta—transformed England from an absolute monarchy into a constitutional one. Several millennia prior, however, the Kingdom of Israel adopted the world's earliest known constitutional monarchy—a kingdom in which the monarch himself is subject to Law. Ancient Israel prototyped other aspects of modern governance also; namely, separation of powers. Priests, prophets, and kings occupied distinct, non-overlapping roles. Additionally, a person who occupied one of these offices was forbidden from simultaneously holding any other; that is, a priest could not also be a king, nor a prophet be a priest, etc.

When a person assumed a role of priest, prophet, or king, he was anointed with oil, thus becoming an "anointed one" or "messiah". (Messiah—or rather, Mesiach (מָשִׁיחַ)—simply means "anointed one" in Hebrew.) Throughout the Old Testament, however, God continually promised to one day send more than simply a messiah, rather: the messiah, the consummation and fulfillment of all the others who had preceded him. The Messiah (definite article, capital "M") would be triply anointed and permitted to overcome Israel's separation of powers; he would occupy a threefold office: Priest, Prophet, and King.
The most recent podcast, "More on Melchizedek", discussed how Melchizedek foreshadowed the Messiah by holding two of those three roles: priest and king. Though the Priest-Prophet-King secretariat, enumerated as such, is not explicitly mentioned in the Bible, Christian theologians since at least Eusebius in the third century have asserted that Jesus claims these three titles. In the 1530s, John Calvin provided the most comprehensive treatment of the "threefold office" (munus triplex in Latin). He and countless others have contributed voluminously to the understanding of munus triplex, but for our purposes, here is a very brief summarization:
Munus Triplex is the threefold office of Priest, Prophet, and King, occupied simultaneously and legitimately, reserved for God's promised Anointed One (Messiah), fulfilled in the person of Jesus. The consolidation of these roles within a single person corroborates God's approbation of the individual and validates his authority delegated from God.
Priests mediate between God and people. They intercede by offering sacrifices to God on behalf of sinners. In the book of Hebrews, its author avouched that Jesus, through self-sacrifice, acted as that mediator: He stood in the gap between sinful man and incorruptible God and brokered a new, restored relationship.
Prophets reveal God's will. In Deuteronomy 18, God vowed to raise up a great prophet, and the book of Acts explicitly equates that promised prophet to Jesus. When we observe the life of Jesus, we see God's will revealed in his teachings, interactions, and very essence.
Kings rule the kingdom and govern the subjects. In 1 Corinthians and elsewhere, the claim is made that Jesus rules the earth. In the blog collection of "Blind Animals", "Parousia", and "The Kingdom of Heaven", we dove deeper into Jesus's reign (including his/its seeming absence) and how followers of Jesus believe that he has complete authority over the entire earth, including even its imperfect administrators.
The Christian philosophy holds that all positions of power—from emperor or bishop, to team lead or HOA treasurer—and those who occupy them ought to adopt a servant mentality. Jesus demonstrated this by washing the disciples' feet at the Last Supper, but through the munus triplex, he continues to serve us every day—offering intercession, revelation, and leadership: the duties of Messiah.
This blog is about the Magna Carta, governance of ancient Israel, types of monarchies; Melchizedek, who was Melchizedek, what is Munus Triplex, Munus Triplex as described by John Calvin, roles of Messiah, what does the word Messiah mean, what types of people were anointed in the Bible; what is the role of a priest, what is the role of a prophet, what is the role of a king; kingdom of Heaven, if Jesus is king then why is the world broken and ruled by bad people; Jesus washing disciples' feet, pedilavium. Hebrews 2:14ff; Hebrews 7; Deuteronomy 18; Acts 3:22ff; 1 Corinthians 15:24-28; John 13:1-17.