Only believers can minister to one another--
Now there are diversities of gifts, but the same Spirit. And there are differences of administrations, but the same Lord. And there are diversities of operations, but it is the same God which worketh all in all. But the manifestation of the Spirit is given to every man to profit withal.
---I Corinthians 12:4-7
But under the clergy system none of this matters, for the people sit mute during the meeting, and only a few considered spiritual from among the congregation are occasionally solicited for participation in the service.
So one cannot tell the believers from the professors, except, perhaps, "after church."
Of course this is what transpired in the 2nd-5th centuries A.D., culminating in "the one, Catholic church" dominating Christianity for a thousand years, while the dissenting (or protestant) churches mostly adopted the same system. Thus, under the clergy system all churches eventually "go to seed." The exceptions–and there are many–are well-known to God, albeit having no sectarian identification that would give them "a name that thou livest, and art dead."
Having no sectarian identification, however, does not necessarily absolve an independent Bible church from the charge of sectarianism, for the simple reason that sectarianism is not only following a man, it is also an imitation of the traditions of men rather than of God. As an example, the Plymouth Brethren divided in 1848 into a sect (the Exclusives), with the other (Open Brethren) churches retaining independency and, at least at the time, their original principles of meeting which aligned with New Testament teaching.
Although the dissenting churches in history did not uniformly, perhaps even characteristically, jettison the clergy system, some of those who did are recorded in E.H. Broadbent's wonderful history, "The Pilgrim Church."