- Were the 12 not only Apostles, but also Bishops (episkop), and Priests (presbyter). ie are the terms mutually exclusive? Are they hierarchical, in the sense that one cannot be a bishop without being a priest, and one cannot be an Apostle (with a capital A) without being a bishop?
Just treating a very narrow topic here, regarding bishop/apostles and priests.
I normally think of it as a differentiation between the role of priest as in exercising the priesthood and the order of priests, as distinct from the order of bishops that we have today. Initially, there was no differentiation between priests and bishops. The bishops in the early church (starting with the apostles) were the priests. Only the order of deacons was distinct from the order of the bishop/apostles.
Much of life in the early church revolves round the liturgy and the liturgy was celebrated every Sunday. As the liturgy was also a sign of communion of the community (i.e., the church), there was initially only one liturgy in each town (which became particular churches), led by one of the Apostles. (there being only one bishop for each church is clear today when several bishops celebrate mass together but only the bishop of the diocese holds the crozier - indicating only one shepherd) The Apostles were the original bishops - which is why until today, bishops take the title of the main town in the diocese. In effect, Christianity was a religion of the city and the people of the surrounding countryside would come into town for the weekly mass and fellowship.
Rather quickly, the Church grew to requiring more liturgy centres in more towns, and the Apostles, individually or collectively, commissioned apostles who had personal knowledge of Jesus (i.e…, received their teachings from Jesus). In a way, you can say the Apostles evolved into apostles. Eventually of course, they started to commission those who had no personal knowledge of Jesus but the apostles vouched for them by the laying of hands and in this way, symbolically transmitting to them the teachings of Jesus - this becomes the Apostolic Succession, which is very important to us as it proves that the our current bishop teaches the same things that was taught by the Apostles and hence Jesus himself. Even Paul took great pains to state that he taught the same teachings as Peter did.
As the congregation got bigger, the bishop in the main town began to commission leaders to lead the liturgy in the smaller towns under him. The newer church (here, used in the sense of the assembly of the faithful rather than a building of worship) would be sponsored by the mother church in a relationship that would eventually become the archbishop-bishop kind of relationship which we today call suffragans.
Eventually though, the Church grew until a saturation point when all the towns had bishops. This was the situation in Italy before the reorganisation (I think in the 80s?) with every small town in Italy having a bishopric that traces its establishment in the early centuries of the Church. As the congregation for liturgy got bigger and bigger, the bishop (by now, very few of whom are apostolic) began to send delegates to conduct liturgical worship for those in the surrounding countryside, particularly for those who are not able to come into town for the weekly liturgy.
As these worship are sacrificial in nature, the delegates were all ordained as priests (in all religions, only priests conduct sacrifice - which is why Protestants who don’t believe in a sacrificial mass only have pastors, and not priests). These priests while having the authority to say mass, remain delegates of the bishop and the mass they say is an extension of that of the bishop. Which is why today, the bishop is always the chief liturgist in his diocese, he is responsible for every mass said in his diocese, no outside priest can say mass in his diocese without his permission, and all masses said in his diocese included a prayer for him.
Initially, the priest-delegate returns to the town after the liturgy but rather quickly, it became obvious that it makes more sense for him to extend his stay in the countryside to tend to the souls there. Eventually, the stay got longer and became more or less permanent and the priest-delegate becomes a pastor, hence the link between the words pastor and pastoral (=countryside).
Of course, the evolution from Apostles & deacons into the triple clerical order was not all that neat or uniform in all places but it was more or less underway in most places by the end of the first century for Ignatius to seemingly use the terms bishops and presbyters interchangeably and sometimes implying more than one bishop/presbyter in a community. (but deacons were always separate). By some 5 decades later, the separation of bishops and presbyter/priests was very clear.
While not everything happens everywhere in exactly the same way I described above, I still find this a very fascinating story which still have an impact on how certain practices take place in the Catholic Church today.
