Who and what is a high priest?
The Bible speaks of many different kinds of priests. In Genesis 14:18 we read of the first high priest that the Bible introduces to us. "And Melchizedek king of Salem brought forth bread and wine: and he was the priest of the most high God." In the context we read that Abraham gave tithes to Melchizedek thus acknowledging him as God's high priest. The book of Hebrews points out that Jesus is a priest after this order of priesthood.
In the Mosaic covenant, God mandates that there be a high priest to intermediate between God (who is holy) and the people (who are sinful). We have a tremendous amount of detail regarding the office of this priest. He was to be of the tribe of Levi of the descendents of Aaron the brother of Moses. Aaron was the first high priest under the Mosaic covenant. This high priest was to consecrate and dedicate himself to the worship of God within the tabernacle and later the temple. The high priest was ceremonially installed into the office per the instructions found in Exodus 29:29 and following. Each new high priest had to wear holy garments and undergo a special anointing (Leviticus 21:10). The high priest was also to wear the vest of the ephod which was a sleeveless garment worn over the upper torso. A description of this item of clothing is found in Exodus 28. In this vest were engraved in various places the names of the twelve tribes of Israel. The vest also had a pocket wherein the Urim and Thummim were kept which he alone could consult. The headdress was of fine linen and inscribed upon the gold plat of the crown were the words, "Holy to Jehovah." This special tunic inscribed with the names of Israel on it represented the nation of Israel where as the headdress labelled "holy to Jehovah" represented the interests of God. In combining the two we see a picture of mediation in the person of the high priest.
Perhaps the most interesting thing about the office of high priest is that he was to enter the most Holy place once a year and offering an atoning sacrifice both for himself and for the children of Israel (Leviticus 16). He was not to wear his priestly garments, but was to dress in pure linen. After the sacrifice he was then to preside over the sending of the scapegoat into the wilderness.
The high priest also had to keep his person pure. One could not be a high priest who had physical defects or deformities. He was to marry a virgin woman of pure character. He was not to defile himself by contact with any dead bodies and he was not to show the signs of public mourning while attending to his duties. He was not to eat anything that had died of itself. He was to wash both hands and feet before nearing the altar. He also acted as a judge for various diseases, for legal questions, and ultimately for questions regarding spiritual leadership.
This is a basic description of who and what the high priest was under the Old Covenant. However, under the New Covenant we have a different kind of high priest. Fifteen times in the book of Hebrews Jesus is named as high priest. The burden of the book of Hebrews is to show that the way of Christ is the better way. That Judaism cannot hold a candle to the blessings that are bestowed on us in Christ. Part of these great blessings is the high priesthood of Jesus. The high priest that we have in Jesus is superior to that of the high priesthood under the Old Covenant because 1) It was after the order of Melchizedek (Heb.5:10; 6:20). 2) Jesus lived a perfectly sinless life (Heb.5:9) 3) He therefore does not need to offer sacrifice for himself daily because he offered up a perfect sacrifice once for all people and all times (Heb.7:27). 4) While the high priest under the Old Covenant went into the Holy Place and then came out, Jesus went into the Holy Place and sat down (Heb.10:12). 5) This makes him a mediator for a better covenant (Hebrews 9:15).
Today we have no system of worship that demands a segregated priesthood. All Christians are considered by God to be priests under the New Covenant (1 Peter 2:5, 9; Rev.5:9). However, we only have one high priest--Jesus the Christ. He is now sitting on the right hand of the throne of the Father and he "ever liveth to make intercession for us" (Hebrews 7:25). As our High Priest, he is both the one who offered the sacrifice for our sins and the sacrifice itself. That one sacrifice makes Him the only High Priest that God recognizes today. As high priest, He was tempted just like we are tempted each and every day (Heb.2:17). He understands both man's side of the issue of sin and God's side of the issue of sin and thereby can act as the perfect mediator. Just as the high priestly garments under the Old Covenant symbolized mediation, so today Jesus embodies mediation. Who is our High Priest? Jesus. What is a high priest? A mediator between God and man.