It is common to mark the beginning of the introspective conscience of the West in the life of Augustine of Hippo

... Augustine made the inner life legible in a way it had rarely been before. He showed that faith ... is a struggle ... The “Confessions” ... taught believers that the interior life matters — that what happens in the private conversation between a person and their conscience is not a footnote to the religious life but its very center. In some ways, this was more revolutionary than anything in scripture itself. ... Augustine made interiority a theological category. Western Christianity has not been the same since. ...

Discussed here.

And yet Augustine arguably is the product of an introspective Western wave which itself had been many centuries in the making.

One could say that the turn to the inner life in the West actually began under the prosaic circumstances of the collapse of the Athenian Empire in 404 BC. 

If Hellenic is the ideal which was lost and Hellenistic its Nachleben and personalization, there are centuries of preoccupation with the experiences of individuals under various aspects which follow after the collapse of classical Athens. These arguably add up to interiority as the rule of the subsequent West, not the exception.

The advent of disorder in the world ended up provoking a broad search for order in the soul, which ultimately worked to the greatest advantage for Christianity.

Notable evidences of this search would have to include, for example, Plutarch's biographical interest in the personal morality of his subjects, or Hellenistic philosophy's general retreat from concern with public life to the vicissitudes of the inner life, as seen in the developments of Epicureanism and Stoicism.

The latter in particular came to dominate elite conviction for centuries, from East to West in the Mediterranean, from Seneca's Letters in the mid-first century evincing his struggle of the will to Marcus Aurelius' self-critical Meditations a century later, a Stoic analogue to Augustine's Confessions later popular in the Greek East.  

The early great Christian authors are nothing if not children of this past, sometimes quite beyond their ken or control, which was surely not the case with Augustine, who was inspired from a young age by Cicero's love of wisdom. While completing his Confessions in 400 Augustine self-consciously borrowed from the Neoplatonist Plotinus, in whom he found the idea of the immaterial soul liberating from the materialism of the Manichaeans.

Combining this abstraction with the allegorical interpretation of the Bible which he embraced from Ambrose of Milan, one could say Augustine was equipped with the spiritual tools necessary for not just his interior project, but for surviving a civilizational collapse which he saw coming in his own time.

The Gothic invasion of the Roman Empire had begun years before the Confessions, in 376, when Augustine was still a very young man of 22. But by 410 Rome had been sacked, in the wake of which he composed The City of God, in which he provided Christians with a rationalization of the catastrophe and an inner retreat from the horrible new reality, an invisible, spiritual city where God was still in control. 

Augustine is nothing if not a spokesman for the experience of everyman from every age, for the little lives of people who turn inward to protect who they are when all is falling down round about them, while some, and even now just like Strelnikov, simply choose to die on the inside before they must die on the outside:

David Bentley Hart finally grasps that the New Testament's apocalyptic communism makes "no sense even in the context of antiquity"

 

Here in The New York Times in "Are Christians Supposed to Be Communists?":

The books of the New Testament, I came to see, constitute a historical conundrum — not because they come from the remote world of late antiquity, but rather because they often appear to make no sense even in the context of antiquity. ... While there are always clergy members and theologians swift to assure us that the New Testament condemns not wealth but its abuse, not a single verse (unless subjected to absurdly forced readings) confirms the claim. ... It was all much easier, no doubt — this nonchalance toward private possessions — for those first generations of Christians. They tended to see themselves as transient tenants of a rapidly vanishing world, refugees passing lightly through a history not their own. ...

[T]he transition was not quite as abrupt as one might imagine. Well into the second century, the pagan satirist Lucian of Samosata reported that Christians viewed possessions with contempt and owned all property communally. And the Christian writers of Lucian’s day largely confirm that picture: Justin Martyr, Tertullian and the anonymous treatise known as the Didache all claim that Christians must own everything in common, renounce private property and give their wealth to the poor. Even Clement of Alexandria, the first significant theologian to argue that the wealthy could be saved if they cultivated “spiritual poverty,” still insisted that ideally all goods should be held in common.

As late as the fourth and fifth centuries, bishops and theologians as eminent as Basil the Great, Gregory of Nyssa, Ambrose of Milan, Augustine and Cyril of Alexandria felt free to denounce private wealth as a form of theft and stored riches as plunder seized from the poor. The great John Chrysostom frequently issued pronouncements on wealth and poverty that make Karl Marx and Mikhail Bakunin sound like timid conservatives. According to him, there is but one human estate, belonging to all, and those who keep any more of it for themselves than barest necessity dictates are brigands and apostates from the true Christian enterprise of charity. And he said much of this while installed as Archbishop of Constantinople.

The whole thing is a splendid summation of the ideas discussed here at this blog, and I wholeheartedly recommend that you read it.