As I am sure you are aware, the Jews had priests. They were a group of Jews set apart from their brothers and sisters. They were of the tribe of Levi and were descendants, specifically, of Aaron, the brother of Moses. However, there is a prophecy in Exodus that there would be a future kingdom in which all of its members would be priests. It is in Exodus 19:6 “You will be for me a kingdom of priests and a holy nation.”
Well, guess what, that prophecy has been fulfilled! As God tells us through Peter, as Christians, all of us are priests. “But you are a chosen people, a royal priesthood, a holy nation.” (1 Peter 2:9) Therefore, all Christians have a priestly role and there is no special, separate priesthood. All of us are ministers. All of us are ambassadors (2 Cor 5:18-20). We no longer need specially chosen or appointed priests because all of us are priests and all of us have direct access to God in heaven. “For there is one God and one mediator between man and God, the man Jesus Christ.” (1 Timothy 2:5) We are priests and we do not need priests to mediate for us.
So, biblically, there is no special priesthood. Yet, the Coptic, Orthodox, Catholic and Episcopalian denominations have priests as “clergy” who do priest-like things for the “laity” like offer a Lord’s Supper which is celebrated as if it were a reenactment of the sacrifice of Jesus.
This is not a biblically authorized practice, to say the least. So, how did we get to this point? The Lord’s Supper is not a “mass.” It is not a sacrifice, but a remembrance. As you might have guessed, there is a historical reason that this false doctrine/practice of anointing “priests” arose. It goes back the the very late first century. By this time, the church had already moved slightly from the biblical admonition on church leadership. In the Bible we are given instructions for the appointing of elders, also called overseers and shepherds. The instruction are given in 1 Timothy 3:1-7 and Titus 1:5-9. In his first letter, Peter uses the three terms, shepherd, elder and overseer (poeman, prebeteros and episkopos) in one passage, making them equivalent. (1 Peter 5:1-4)
By the end of the first century, many churches started appointing, essentially, a head elder. This head elder was called a bishop, using the Greek word episkipos (bishop comes from the Latin). Below the bishops were the elders (presbyters in Greek). Biblically, the shepherd/bishop and the elder are the same person. However, by the second century the two roles had been divided. Later there were bishops over the bishops, known as archbishops and metropolitans over the archbishops and even popes over the metropolitans.
Here is what happened from there. The elder/presbyter role gradually evolved into priests. By the late fourth century the doctrine of sacramentalism had developed in both the East and the West of the church. By this time, priests, who used to be called presbyters, were performing a sacrifice-like Eucharist which evolved over time into a Jewish-like priesthood which made sacrifices for the common people and who made intercession for the common people. Essentially, the Roman Catholic, Coptic and Orthodox churches relegated to a “priesthood” the role that the Bible gives to Jesus, which is to intercede for us and to make sacrifice for us.
What you can see from this very brief historical outline is that the priesthood evolved gradually over a few hundred years from biblical leadership roles. The fact that these churches separated the role of the overseer from the elder is a relatively minor matter, in my opinion, but the fact that they gave them a special, sacramental role which is reserved for Jesus Christ is a very big problem indeed, at least as far as I see it, but that is what happened.
I hope this helps.