In his death, Jesus became the priest of all humanity and creation.
1. So the first office of Christ that we considered was that of prophet. Now we consider his office as priest. 
We might argue that Jesus was priest before his death, but clearly the focal work of Jesus as priest took place on the day that he died on the cross. It was on this day that he accomplished atonement, which is to make up for some wrong done by way of an offering. Atonement has to do with making amends and thus with reconciliation between a human and God.
The means of atonement is some sort of offering or sacrifice to God. The background here are the countless animal sacrifices that were made in the ancient world to appease the gods, to make them happy and to diminish their anger. In the Old Testament, the book of Leviticus gives instructions to the priests of Israel on how to make sacrifices to God, some of which were done to give him thanks and praise rather than to appease his wrath.
2 The New Testament book of Hebrews suggests that these sacrifices were never intended to actually work (Heb. 10:1-4). Hebrews indicates that the sacrifices of Leviticus were foreshadowings of the one effectual sacrifice of Jesus on the cross.
This is a significant point because there is a tendency to overplay Hebrews 9:22, which says that there can be no forgiveness for sins without blood. Yet Hebrews clearly indicates that none of the blood of the Old Testament Law actually did take away sin. And the one blood sacrifice that did take away sin--that of Jesus--ended the need for any further blood sacrifice: "By one sacrifice he has made perfect forever those who are being made holy" (Heb. 10:14).
In other words, there has only been one effectual blood sacrifice in all of human history, and its consequence was to end the need for any blood sacrifice.
There are two basic ways to take this startling claim, that none of the Old Testament sacrifices actually did anything. The first is the traditional way, namely, that all those millions of animal sacrifices in the ancient world were elementary school lessons God instituted to get humanity ready to understand the death of Jesus. The problem here, of course, is that none of the people offering them actually got the point until the first century AD. In this case, the object lesson of a million sacrifices basically went to naught.
The other interpretation seems more likely. It might not deny that God fully allowed, perhaps even directed the origins of animal sacrifice. It is easy enough to argue that animal sacrifice corresponded to a deeply felt need on the part of humanity to be reconciled to God, not to mention some primal sense that such reconciliation merited sacrifices of immense proportions. Certainly God allowed the practice to arise, whether he planted the idea or not.
The question is how important this practice was to God. Was this practice essential for God or useful to God.
In the Old Testament, God used the prevalent practice of animal sacrifice to set Israel on a course toward Christ. But, of course, sacrifices had been around for thousands and thousands of years before Israel. The first approach places a strong emphasis on the need for sacrifice (even though they were completely ineffectual, according to Hebrews). The second suggests more that God used a practice that pointed toward certain truths rather than it being necessary or essential.
We may see this dynamic of "using" common religious practices in the sanctuaries of Israel. The sanctuary of Israel was not unlike the sanctuaries of other ancients. Again, it is easy enough to see how the notion of holiness would arise naturally as humanity contemplated proximity to God. It makes perfect sense that, as you came in closer and closer proximity to a god, the space would become more and more sanctified (made holy), to where only certain people would be allowed in closest proximity.
But in the second perspective, which I hold, God uses these notions in order to do away with them. "The Most High does not live in houses made by human hands" (Acts 7:48). God allows practices to arise that embody the fundamental human need for God. He uses them until Christ comes to provide true reconciliation. Then those practices of sacrifice in sanctuary by priest are no longer needed. The reality those practices embodied and foreshadowed is accomplished.
3. This is the argument of Hebrews. Christian tradition had considered Christ's death as a sacrifice from the very beginning. Indeed, it is quite possible that Jesus himself suggested this metaphor even before his death, at the Last Supper (cf. Luke 22:19-20).
When Romans 8:34 says that Christ sits at God's right hand interceding for us, it likely refers to Jesus serving as a priest for us, although Paul does not use the word priest here. But some Christian has clearly extended Christ's role beyond that of being the sacrifice to being a priest as well.
This trajectory becomes full blown in the New Testament sermon we call Hebrews. Hebrews not only considers Jesus the sacrifice. It not only considers Jesus a priest. It considers Jesus the priest who offers himself as a sacrifice. Several images of sacrificial atonement from the Old Testament are brought together to see Christ as the priest to end all priests.
The most powerful of these images is Christ as the high priest, like the earthly high priests of Leviticus who went into the Most Holy Place in the earthly sanctuary one day a year on the Day of Atonement (cf. Lev. 16). Christ is now the true priest who is the reality to which all other human priests have ever pointed. He is a "priest after the order of Melchizedek" (Heb. 7), an order of priests superior to the Levitical priests.
His death is the true, effective sacrifice, in contrast to all other sacrifices in history (cf. Heb. 10:1-4). He enters heaven itself (Heb. 9:24), the true sanctuary (Heb. 8:1-2), rather than some earthly shadow or sketch (cf. Heb. 8:5).
4. Therefore, when we say that Christ holds the office of priest, we are saying that he is the one mediator between God and humanity (cf. 1 Tim. 2:5). "I am the way and the truth and the life. No one comes to the Father except through me" (John 14:6).
We will discuss the atonement of Christ in more detail in a later article. For now we want to point out that Christ is the one who offered himself as the sacrifice to end all sacrifices, the definitive means of reconciliation between God and the creation. "Salvation is found in no one else, for there is no other name under heaven given to mankind by which we must be saved" (Acts 4:12). Again, we will explore the nature of salvation more extensively in later articles.
No human priest is therefore necessary, although God does have ministers of reconciliation such as Paul was (cf. 2 Cor. 5:18). No human priest or pastor is necessary, but they may very well be helpful and useful. Indeed, God has appointed his Church to be a "kingdom of priests" for the world (cf. 1 Pet. 2:9; cf. Exod. 19:6).
Meanwhile, Christ sits at the right hand of God as intercessor for us (Rom. 8:34). We probably should understand the focus here to be intercession for our atonement rather than the more general intercession that the Holy Spirit does for us (cf. Rom. 8:26). Hebrews 4:14-16 captures this role of intercession for our forgiveness well:
"Therefore, since we have a great high priest who has ascended into heaven, Jesus the Son of God, let us hold firmly to the faith we profess. For we do not have a high priest who is unable to empathize with our weaknesses, but we have one who has been tempted in every way, just as we are—yet he did not sin. Let us then approach God’s throne of grace with confidence, so that we may receive mercy and find grace to help us in our time of need."
In his death, Jesus became the priest of all humanity and the creation, the only effective mediator between humanity and God.
Next week: C5. In his resurrection, Jesus became the king of all humanity and creation.
 These offices, in my opinion, all relate to things that Jesus did and events in Jesus' mission. We most literally understand these offices as metaphors for his work, rather than his work being a function of his offices. The offices are abstractions of the events in Christ's life and mission.