In his 2014 volume The Original Bishops, Alistair Stewart writes that when the early Christians set about finding language to describe their institutional life "[s]imilar societal institutions, such as synagogues and other associations, would be the primary source of language, whereas scriptural usage and familiarity would be a secondary filter only" (p. 134). As stated, it seems to be axiomatic, and that leads me to query whether the axiom is true. I'm not entirely persuaded.
I think that we need to remember the degree to which the first generation or two of Christians were convinced that scriptural prophecy was being fulfilled in their midst. They were, I think, quite convinced that the church in Jerusalem was fulfilling certain prophecies about the eschatological Zion. They seem to have understood the Diasporic missions in terms of prophecies about Zion constituting a light to the nation. Given such a situation I don't think it at all improbable that early Christian institutional language would be guided more by scripture than by "similar societal institutions." Indeed, I'm not certain whether in their minds there were any similar societal institutions. Related to this we must remain cognizance of the fallacy from analogy: just because Christians use the same terms as other groups does not mean that they used them in the same way. They might have, they might not. "Occupy" meant something quite different to the protesters who gathered in Zucotti Park in 2011 than it does to military planners in the Pentagon.
Now, let me be clear: I am not making any statement regarding whence Christians derived terms such as episkopos, presbyteros, or diakonos. I am rather questioning the axiom Stewart seems to articulate on p. 134 of his book. My fear is that Stewart represents here what the anthropologist Evans-Pritchard described as "If I were a horse" thinking. "If I were a horse I would like to lie in the sun." "If I were a Pacific islander I would behave thus and so." "If I were an early Christian I would use language in this way or that." Such approaches characterized ethnography and ethnology prior to the emergence of modern fieldwork in the 1910s, which had the incredible idea that if one wants to know how Pacific islander behaved one should spend some time with south Pacific islanders, preferably on their Pacific islands. That's what Malinowski did (somewhat by accident: he was stranded in the region because of shipping disruptions during the First World War), thus becoming the father of modern anthropology and ethnography more generally. That, ideally, is what historians do, mutatis mutandis. Rather than decide a priori that early Christians would prefer language drawn from extant societal institutions rather than from scripture the historian reads early Christian writings and gets a sense of how they are using language. She or he reads the material from the broader literary and inscriptional environment in which the early Christians lived. Then, she or he formulates an a posteriori hypothesis on the matter.
Let me also be clear: despite the above misgiving, Stewart's work is a must-read for anyone interested in early Christian social history.