My basic understanding is that in the process by which Jesus's work and teaching became "Christianity" - something simple and inner, became something complex and outer.
With Christianity; Jesus's teachings became an "outer" set of laws/ rules embedded in a structure of government, with "the Christian's" duty being, primarily, obedience.
Christianity defined being-a-Christian as obedience to the rules and laws of The Church (and/or of the Christian State).
As part of this, Christianity became a "system" of dos and don'ts - a system of rules that were - overall and on average - Good...
Yet, at the same time, external rules (no matter how many, and how perfectly obeyed) can never, in principle, capture the essence of being a follower of Jesus Christ... Which is ultimately an inner matter - a matter of motivations.
This has always been obvious enough to thoughtful Christians - obedience to the structure is never enough; and the rules can only (at most and at best) serve as "pointers" towards being-a-Christian.
Furthermore, the rules - by their nature - are incomplete, to some extent incoherent, and have exceptions.
Even the best rules do harm, as well as good. For instance; rules that benefit the majority, in the long term; will often harm a minority (which may be a large minority) in the short term. And the harms may be immediate and certain, while benefits are delayed, and somewhat conjectural.
In other words, the essence of Christianity is personal, and private; and always has been.
In a strict sense, therefore; all real Christians are "Secret Christians" - Christians in their hearts; and this subjective reality cannot possibly be "captured" by even the best sets of Good rules; even when these rules/laws are most ideally administered and obeyed.
But in practice; the rules were very much more imperfect than ideal, there was corruption in their administration; and plenty of people were hypocrites - who exploited the letter of the law to subvert the Christian spirit behind the law.
Yet it was usually asserted that the real and true Christianity was its laws and institutions. Or, that this must be the case in practice.
What happened in private was therefore down-rated to merely subjective - and the objective fact of the actual religion was made the observable, the measurable, the societal.
Secret Christians were relegated to an idea realm of fantasy; ignored, regarded (often accurately) as an excuse for apostasy - and so forth.
So Real Christianity was in practice reduced to what was public, what was legal, what was political...
And thereby Christianity was made ripe for destruction!
The situation was that real Christianity was said (implicitly and in practice, even when officially denied) to be the rules, laws and institutions.
Yet exactly this actuality of Christianity was very imperfect - even in theory, and even at its best it was incomplete and probabilistic; and Christian rules and laws did significant harm, even when they did overall Good.
Over several generations, over the past couple of centuries; the rules and laws of external Christianity were analysed, dissected, subverted - and they were significantly discredited as Not Good Enough.
Having been proved inadequate -- at least, proved to be incoherent, incomplete, and significantly harmful to the satisfaction of the ruling and dominant classes; these "Christian rules" were increasingly confidently seen as A Problem (indeed seen as The Problem), not as an answer.
Christian rules and laws were seen as not reformable; but as something we would be better rid of.
And once the rules and institutions of Christianity evil were seen as a problem; then the stage was set for the incremental inversion of these rules, and the take-over or destruction of the church institutions by the governing ideology of hedonic materialism.
For instance; the rules of patriarchy were inverted to feminism; laws encouraging and enforcing chastity was inverted to "free love", and so forth.
My point here is that - in the space of about 150 years - The West has gone from a set of net-Good but imperfect and partly-harmful "Christian" rules; via a stage of critique and subversion of these rules; to the current situation in which there has been a value-inversion.
The current ideology is one that is orientated against the rules, laws and institutions of what was defined as "Christianity"; and which came to be regarded as intrinsically limited, hypocritically administered, and actually harmful - albeit usually harmful in a minority (whether large or small) of applications and instances.
With this behind us; we cannot, and indeed should not try to, return to the pre-current-ideology System of rules/ laws/ institutions...
Even though the rules and laws of Christendom were indeed better than the present situation overall and on average.
The traditional externally-defined Christianity of rules/ laws/ institution has been discredited - discredited in theory, as well as in practice.
The problems of the past are just too obvious, and too well-known, for sufficient (and sufficiently widespread) motivation to restore it (even if that were possible).
But the Secret Christianity, of which we can read in the Fourth Gospel, remains as ever it has.
This is and was a personal and private Christianity (or following of Jesus) that existed without (and before) there was church, scriptures, theology, or traditions.
Secret Christianity is still the real thing, un-capturable by any set or rules and laws; and immune to any institution - and attainable whether the system is for net-Good, or against it...
Just as it was during the ministry of Jesus Christ.
