Nevertheless, many non-theologians still refer to what “the Church” does or teaches when they mean what the Magisterium does or teaches
Just as the emperor of Rome protected the citizens of Rome through many agents (generals, armies, governors), Christ commissioned agents to act on Christ's behalf to save souls . Christ saves Christians, but Christ saves Christians through the Church. Thus, one needs the Church. The belief was that Christ called many to follow him, but commissioned a few as leaders to act on his behalf in his absence. These leaders in turn commission successors, such that even today bishops can claim to have been made a bishop by someone who was made a bishop by someone who was made a bishop by… all the way back to Christ.
Take for example the Eucharist. Christ gathered his disciples and instructed them to break bread, which becomes his body. Variously conceived, eating this body of Christ meant participating in the Church, understood as the body of Christ, and participating in the resurrection of the body of Christ. One needs to eat the bread of life in order to have eternal life. In the earliest Jesus movement perhaps any gathering could perform this ritual with or without an agent appointed by Christ. As the Church became institutionalized and structured, not just anyone could take the place of Christ in this ritual, only someone who was duly appointed (no matter how long that chain of appointment may be). In a very real sense, the Church had a Monopoly on salvation. Even if the ultimate supplier was Christ, in practice it could only be obtained through official channels.
This is the core of what Martin Luther rejected in the 16th century, as we shall see in a few weeks. The Catholic Church did not accept all of Luther's points, but it did reform itself in response to some of his points. The above way of understanding the role of the Church as mediator of Christ's salvation is true of the Catholic Church in the Middle Ages but not today .
Catholic theologians in the 21st century will say that all the faithful are the Church, and the leaders are part of the Church. The Magisterium is the teaching authority of the Catholic Church, namely the bishops in their role of clarifying and teaching proper beliefs and practices. Although theologians today would not say that the Magisterium, the Vatican, or the Pope are “the Church” any more than I am, in the Middle Ages there was a tendency to view the Magisterium as being the real Church, acting on behalf of Christ, in contrast to the followers.
Theologians such as Augustine had a very high ideal of the Church as the body of Christ and bride of Christ. However, they were not unaware of the frailty of the humans that made up the Church. There was never a generation in which there were no corrupt priests or bishops. There have been different views of what to do about it.
One of the early scandals in Christianity was bishops who compromised in the face of persecution. Christianity held the idea that faith is more sacred than life, and one should choose death (martyrdom) rather than renounce Christ visit the site here or worship the emperor. Many lived up to that standard, but many others facing a horrible death gave in. The question was what to do with those people once the persecution ended. The Donatists argued that someone who sinned in such a way had permanently lost the Holy Spirit and could never again exercise leadership of the Church. They thought the Church had no room for sinners, and they preferred a small Church with no tolerance for shortcomings.