These three offices are part of Christ’s role as Mediator between God and men (1 Tim. 2:5). There is an obvious need on the part of sinful humanity for these roles of Christ. We need truth because we are foolish and unwise (prophet); we need our sins put away and access to God because of our damning guilt (priest); and we need to be rescued from Satan’s dominion and be ruled in our hearts and minds (king).
There were prophets, priests and kings in the Old Testament order established by God. But, God did not ordain that all these offices be fulfilled by a single individual simultaneously. The priests came from the tribe of Levi. The kings came from the tribe of Judah. Prophets could come from any tribe. Isaiah was a great prophet, but not a priest. David was a prophet and a king, but not a priest. Zacharias, the father of John the Baptist, was a priest who also prophesied, but he was not a king. A painful example of a man who tried to take upon himself one of the offices that did not belong to him was King Uzziah (2 Chron. 26:16-21). The uniqueness and glory of Jesus Christ is seen in His fulfilling perfectly all three offices: prophest, priest and king.
The title ‘Christ’ means anointed one. In the Old Testament, there are many examples of individuals being anointed with oil, as a ceremony of being Divinely consecrated (set apart) to a certain office. Moses anointed Aaron and his sons to be priests. Samuel anointed young David with oil, since he had been chosen by God as king of Israel. Elijah anointed Elisha with oil, as he was to take up the role of prophet upon Elijah’s departure from this life. God the Son taking on human nature, Jesus of Nazareth, is God’s Anointed One. He has been chosen, ordained by God as Mediator. He has been consecrated by God as Prophet, Priest and King. As Prophet, to speak and reveal the will of God; as Priest, to offer Himself as a sacrifice making satisfaction for sin and to represent the people of God; as King, to rule and reign over the people by His word and Spirit. (Passages on Christ being anointed by God to His work: Psalm 2:1-6; Heb 5:1-6; Heb 1:8,9, Acts 10:37-38).