The Bible teaches that all of Jesus Christ's followers are priests, but after His early followers died off, the concept changed due to insecure, short-sighted leaders who wanted to control the work of God. In practical terms, the leaders little-by-little monopolized power, the places of fellowship and the priesthood. This has led to suppression of the work of God and a form of religion that is different from what Jesus taught. The priests of Jesus Christ were meant to be free, like the wind. As Jesus taught, "The wind blows where it wishes, and you (sg) hear its sound, but you do not know where it comes from or where it goes. So it is with everyone who has been begotten by the Spirit." (John 3:8 SCS)
The Bible teaches that all of Jesus Christ's followers are priests. (See 1 Peter 2:9, Revelation 1:6 and Revelation 5:10.) The concept is borrowed from the Old Testament, where certain followers of Yahweh served has His representatives on earth, living holy lives and teaching his ways, while also praying for others and making sacrifices for them. However, in the New Testament, the work of God is intended to go beyond the borders of Israel and extend outward to all the earth, so the early Christians were all priests, and the Holy Spirit raised up specific people to equip them to be good ones. (See Ephesians 4:11-13.) There was no institutional hierarchy at all, nor did God intend for there to be today.
The Bible also teaches that the only hierarchy in the Church is based on roles, not institutional offices. All believers are to submit to God (James 4:7) and to one another in the fear of God (Eph. 5:21), younger men should submit to older men (1 Peter 5:5), wives should submit to their husbands (Ephesians 5:22-24) and children should submit to parents (Ephesians 6:1). It's all based on relationships in the community, not some man-made certification. In fact, most men in a free society choose their own elders. For example, when men face a life problem, do they go to a priest or to a trusted male friend who has exemplified wisdom in life affairs? In many churches today, priests are more like hired hands than shepherds. (See John 10:1-15.) In some churches, they are even predators! This may be why Jesus hates the deeds and doctrine of the Nicolatians (Revelation 2:6, 3:15) - because in Greek "Nikolaḯtēs" means "to be victorious or rule over the people." This is exactly what "clergy" have often done throughout history in clergy-laity caste systems.
Jesus made it clear that He was transferring the Kingdom of God from the well-defined and predictable nation of Israel to a group of unpredictable people from every tribe, language, people and nation called the Church (Matthew 21:43, Ephesians 1:22,23, Revelation 5:9,10). His goal was clear: He wants His people to have intimate personal relationships with Him and to love each other (John 10:27, 15:1-17). He wants His followers to have unity without union, because union is often the enemy of unity. For example, He never told them to form institutions, set up a clergy-laity caste system or suppress the role of the Holy Spirit in raising up gifted people to equip His followers for being good priests. Instead, He wants His followers to be faithful to Him, be guided by the Holy Spirit and be unpredictable like the wind:
Jesus answered: "Most assuredly I say to you, unless someone is begotten by water and Spirit he is not able to enter the kingdom of God. That which has been begotten by the flesh is flesh, and that which has been begotten by the Spirit is spirit. Do not be perplexed that I said to you, 'You (pl) need to be begotten from Above'. The wind blows where it wishes, and you (sg) hear its sound, but you do not know where it comes from or where it goes. So it is with everyone who has been begotten by the Spirit." (John 3:5-8 SCS)
Jesus Christ also didn't want His follwers to be slaves to a hierarchical system that leads to unhealthy competition and unfair privilege that takes attention away from Him and His Father:
"But you (pl.), do not be called 'Rabbi'; because your Teacher is one, the Christ, and you are all brothers. And do not call anyone on earth your 'father'; because your Father is one, He who is in the heavens. Neither be called leaders/guides; because your Leader is one, the Christ. On the contrary, the greatest among you must be your servant. And whoever exalts himself will be humbled, and whoever humbles himself will be exalted. (Matthew 23:8-12 SCS)
Today, we see millions of Roman Catholics calling themselves "priests", setting themselves up above others by means of their titles, even though many live in immorality and/or luxury. Although they may teach on a theoretical level that all Christians are priests, on a practical level they suppress that from happening. The formalization of the priesthood followed the formalization of church gatherings. Although most churches were originally just small groups of people meeting in homes focusing on God and serving people, eventually churches became became larger, and buildings were erected. The informal gatherings that Jesus and the early Christians enjoyed turned into formal gatherings which resembled Jewish synagogues or even pagan temples.
How did all this come about?
The paganization and monopolization didn't occur overnight. It happened gradually over time. It started when good men failed as leaders. Yes, good men make mistakes. Sometimes they simply trust themselves rather than God. Sometimes they implement short-term policies without thinking about the long-term negative side effects.
In order to protect Christians against heresy and division, church leaders in the second century AD decided that they had to control the work of God. First, they added to Scripture by establishing a clergy-laity caste system with laity on the bottom, deacons above them, presbyters above them and bishops on the top. (See The Epistle of Ignatius to the Smyrnaeans I.) Next, they decided to add to Scripture by establishing "authorized" meetings and condemning all meetings that were "unauthorized." They seemed to believe that God had given them exclusive rights to decide where the Holy Spirt could operate and whom He could operate through. They came up with the clever idea of "apostolic succession" in which they alone get to pick leaders. In other words, they wanted to totally control the wind! (See The Treatise of Irenaeus of Lugdunum against the Heresies.) It basically outlawed informal gatherings in home or other places and led to persecution of anyone not operating under their umbrellas. (See The Unity Of The Church By St Cyprian Of Carthage.)
When Constantine became the Roman Emperor, it became even worse, as he merged the institutional church and the state for political reasons. As time passed, the Roman Church became more and more worldly-minded and materialistic. Eventually, it was infiltrated by unbelievers who came into the church and rose to leadership positions. It became so corrupt, that it has actually persecuted and killed millions of true Bible-believing Christians throughout history who didn't want to go along with their sinful monopoly.
Ever since the days of Martin Luther, many Protestant leaders have identified the Roman Catholic Church as Mystery Babylon, the Mother of Harlots and Abominations of the Earth, as described in Revelation 17. Throughout history, many Roman Catholic priests have been fornicators. Today, many are homosexuals, completely unjfit for service in the Kingdom of God, and the whole world knows it.
Today, the leader of the Roman Catholic Church is often called the Pontiff Maxiumus, which was a title given to Roman emperors, who were often considered to be gods. The title originated with Babylonian kings, who were descended from Nimrod and served as both kings and priests of the pagan Babylonian Mystery religion. They derived their power from Satan. So does the leadership in the Vatican today.
Jesus Christ taught:
"Beware of false prophets who come to you in sheep’s clothing, but inwardly they are ravenous wolves. You will know them by their fruits. Do people gather grapes from thorn bushes, or figs from thistles? Just so, every good tree produces good fruits, but the rotten tree produces evil fruits. A good tree cannot produce evil fruits, nor can a rotten tree produce good fruits. So every tree not producing good fruit is cut down and thrown into the fire. Therefore, you will know them by their fruits. "Not everyone who says to me, 'Lord, Lord', will go into the kingdom of the heavens, but he who does the will of my Father who is in the heavens. Many will say to me in that day, 'Lord, Lord, did we not prophesy in Your name, and cast out demons in Your name, and perform many mighty works in Your name?' And then I will declare to them, 'I never knew you; depart from me you practitioners of lawlessness!'" (Matthew 7:15-23 SCS)
And I heard another Voice from heaven saying: "Come out of her, my people, so as not to participate in her sins and so as not to receive of her plagues. For her sins have reached to heaven and God has remembered about her her iniquities. Render to her just as she rendered to you; yes, pay her back double, according to her deeds; in the cup that she mixed, mix double for her. To the extent that she glorified herself and lived luxuriously, by so much give her torment; because in her heart she says, 'I sit a queen, and am not a widow; and I will certainly not see sorrow'. Therefore her plagues will come in one day—death and sorrow and famine—and she will be burned up with fire; because the Lord God who has judged her is strong." (Revelation 18:4-8 SCS)
The good news is that God is bigger than man and has continued to raise up people to serve Him outside of the Roman Catholic Church. Although other churches tend to become institutionalized and worldly and corrupt, God continually uses His faithful priests to do His work quietly all over the world. If you want to follow Jesus, find a small group in which you can actually talk to the people and get to know them, prefably in homes. As we get closer to the return of Jesus Christ, we can expect persecution to spread all over the world, so small groups will one day be the preferred way of gathering for the saints of God. And every member will once again be a priest.