So far as I'd understand it, a first century Christian had no organized church.
I'm not sure that's quite accurate.
Acts (c80AD) shows the actual institution of an administrative structure — it appears the early Church lived the common life, with the distribution of goods for the benefit of all (Acts 5). By 160AD Rome had over 1,500 widows and orphans under its protection.
Sadly, in Acts 6 we see the signs of dissent ... it would appear that all are created equal, but the Jews are more equal than the Gentiles, and were receiving the lion's share of the social outreach programme ... so the Diaconate was established (liturgically as well as administratively) to make sure everyone got a fair deal.
The Bible wasn't canonized ...
The canon wasn't dogmatically defined until the Reformation!
and the council of Nicaea hadn't occurred until well after that. This was when the main doctrines were worked out and what was considered proper vs. heretical were delineated.
But that does not mean the doctrines were unknown before then ... quite the reverse. At Nicea (325AD) the main doctrines were 'ratified', but they had been the common teaching for over 200 years by then. There was certainly a move towards 'standardisation' but that is not necessarily a bad thing.
The doctrines of the Eucharist, the Incarnation, the Trinity ... were all in place well before Nicea, and was the common stock of the people.
The notable exception is the clause inserted into the Creed at the suggestion, supposedly of Constantine, but actually by his theological adviser, the bishop Ossius, of the term 'homoousios' — 'of one substance'. This was to affirm the consubstantiality of the Son and Father beyond dispute — and it failed magnificently, as the subsequent Arian disputes testify.
There was an amazing variety of Christians immediately after Christ's death, most of them blending his teachings (or what they could find out from the hearsay, as there was no canonized text) with whatever their prior religion had been, be it Judaism, Roman Paganism, or something else. There were gnostics and so on.
Indeed so. many forget, or do not know, that Jesus sent out '72' disciples to preach in His name before His final journey to Jerusalem, so these preachers could not know of the mysteries that would be revealed in the Passion and subsequently, nor would they have had such an intense and intensive exposure to Christ.
I think people couldn't be that picky about what was the "right" sort of Christianity until Romans stopped executing them.
Nicea was the first 'ecumenical council' largely because it was impossible to gather the bishops together whilst the faith was proscribed.
As is the usual human condition, in-fighting occurs once there is no outside enemy to bind us together. Ever since Christianity became a state-endorsed religion, it had the luxury of disintegrating into bickering sects rather than existing as a diverse but perhaps less acrimonious family.
Sadly so ... indeed, it seems Jew and Gentile had hardly time to draw breath in the common faith before they fell out. But we should not assume this to be universal.
As a tutor of mine once remarked ... it's not surprise Christianity survived the persecutions, but it's a bloomin' miracle that it survived becoming the state religion!
As you know, I've fought many critics here who lay the fault of everything wrong with Christianity at Nicea. This is, largely, just bad history, propaganda and assumption.
I think the 'real damage' came later, after the 5/6th centuries, when the emerging global institution modelled itself on the Roman Empire ... that (I'm guessing) is a much richer seam, but will need a much finer comb, and a much finer sensibility attuned to Catholicism.
If one is an honest and open-hearted Catholic one will pick up the resonance of error long before it manifests. But I'm guessing here.
Though it seems that even in Paul's day there was plenty of disagreement about an awful lot of stuff ...
Even to the attempt at assassination!
... so perhaps there was never unity to begin with and the unity will (hopefully) evolve out of the church.
I think that unity will be the stuff or miracle rather than any human methodology.
But I think it likely that a first-century Christian may not have even found other first-century churches recognizable as Christianity.
I think you might be surprised. The fundamentals are there ... Baptism, the common life, the Eucharist. These were universal among the churches. The letters of Paul were copied and sent to the other churches, as were letters from various bishops (Clement of Rome to Corinth, for example) ... there was by the close of the first century a tradition of writing to the churches.
I accept there was diversity, from orthodox to heterodox to heresiarch ... but the main line was far more widespread than you might suppose.
And certainly, just given the cultural differences alone, it's unlikely a first-century Christian would recognize any modern Christian sect as familiar.
Of course ... but cultural differences aside, if we look at doctrine and teaching ... then a first century Christian would have felt at home within the Catholic and Orthodox patriarchies ... and of course the early schismatics, Nestorians and so on ... but once we reach the Reformation, then one crosses into another world alien to the early spiritual inspiration.
After all, in the time immediately following Christ's death and resurrection, most "churches" would resemble Bible studies far more than any church today, with the occasional traveling apostle if you were lucky.
House churches, yes ... but it's not the walls, its what goes on within.
Much of early Christendom, from what I understand, was underground due to martyrdom. I doubt they had cathedrals, pianists, organs, choirs, priestly vestements, or any of the trappings we have now... and trappings that I think are lovely and invoke a certain mysticism.
Oh, I'm not so sure. They had the Temple, for example. So whilst there were house churches and catacombs, there would have been a hankering for the sung liturgy, the mysteries ... and we can tell from early iconography and catacomb graffitos that there was already a rich symbolic language that would have adorned vestments etc. had it been allowed.
My archaeological and anthropological influenced mind just can't wrap my head around folks who try to get "back to the origins" of any religion, be it those that want to return to 1st century Christianity or the Pagan reconstructionists. If it floats one's boat, fine, but I'm highly skeptical at the ability of any person to really crawl inside the worldview and life of a person who lived 2000 years ago.
Oh, I quite agree ... but that does not mean we should not try!
The Ressourcement Theology that emerged in the last century continually unearths the richness of early and Patristic thought ... always tempered by the necessity to observe that we are looking from a different mileau ... but this is just the point, we might not know all, but we know enough to know that 'contemporary' or 'new age Christianity' is so far removed from the early image, so clearly reflects the relativism that is the governing philosophical principle of its age ... so while we may not be able to think as they thought, we can come to know enough to know they certainly did not think as many like to think now.
On a personal note ... and I am sure you will know what I mean ... if there is an affinity then there can be a communication that reaches beyond the logical and reasoning faculty.
Thomas