The thought that "nothing is sacred anymore" occurs to many and seems to suggest Modern society has lost something important to culturally shared purpose. Somehow, the absence of a 'sense of the sacred' prompts people to feel lost, diminished, less significant. If that is correct, what is this condition of 'being sacred' that feels 'absent?'
The word sacred carries such meanings as "hallowed, consecrated, or made holy by association with divinity or divine things or by religious ceremony or sanction." It derives from from Old French sacrer, translated as "consecrate, anoint, dedicate" and Latin sacrare, "to make sacred, consecrate; hold sacred; immortalize; set apart, dedicate." Here there appears some relationship between reference to divinity or spirit and a status of being 'set apart' and 'made holy.' The word holy carries similar meanings, but is thought to once have meant "that which must be preserved whole or intact, that cannot be transgressed or violated," with connections to the word health, and derives from the PIE root kailo-, meaning "whole, uninjured." The word divine is defined as "of, from, or like a god." Thus sacredness indicates association with divinity or spirit, with creative or animating agency, that set something 'apart' from ordinary status as related to such agency.
Three Sacreds: Spiritual, Social, Experiential The word sacred has two common contemporary usages. One indicates association with divinity in general (gods, goddesses, spiritual powers), or more particularly to religious practices and doctrines related to notions of 'the divine.' The other usage indicates a condition of great importance or high status that takes precedence over all other concerns. That meaning implies great respect, high status, or reverence without reference to divine or spiritual concepts. In both aspects, sacredness is a condition of 'the highest importance' and thus one that tends to be regarded as 'above' or 'beyond' doubt and questioning -- as 'not to be transgressed' and perhaps fundamental to the 'wholeness' or 'health' of life. This double usage reveals how there can be a 'sacred status' with or without direct spiritual and religious references. Thus a society can regard a national flag as sacred even though the flag is not a direct spiritual symbol. Nonetheless, that more secular use of the word sacred derives historically from pre-modern usage of it as exclusively referring to something divine or spiritual.
So, though modern societies have become politically secular, with government and social systems lacking direct connection to religious concepts, some 'sense of the sacred' has been preserved. Some people consider principles of democratic government or human rights to be 'beyond question,' of the highest importance, and the very foundational justification of society, thereby 'sacred,'
With this usage in mind, we can think of two related 'sacreds.' What appears as the older one indicates spiritual and religious references to 'willful forces' that animate the world, thus are of supreme importance. The second is to ideas, practices, and beliefs that are granted supreme social or cultural status. We can term these the 'spiritual sacred' and the 'social sacred.' In pre-modern times the two would have been closely linked. Earlier societies tended to be organized around spiritual or religious concepts that imbued both human experience and social systems with 'greater meaning.' Governance by monarchy was typically validated by linking it to religion and god/s. Thus, the lament, 'nothing is sacred anymore,' seems to suggest a sense of loss over the dissipation of cultural values that are universally regarded as of supreme importance, both in terms of the spiritual sacred and the social.
Then there is a third aspect of sacredness to consider. That is the experiential. What is it to personally experience sacredness? What is the tangible 'feel' of it? Following the above thoughts, the spiritual sacred would seem to be a feeling that something like a spirit or god is 'present,' The social sacred, then, suggests feeling that some place, object, concept, or practice gives one a feeling of supreme significance and importance, of creative agency, even in the absence of overt spiritual references. Here we can try to distinguish between immediate experience and intellectual belief in an idea or concept. That is, one might have a sense of the sacred in response to some tangible phenomena not overtly designated as sacred or in response to an established, socially confirmed, idea about what is 'officially' sacred. But just what is this experience like?
Experiential Sacredness and Numinosity: The word numen specifically refers to the quality a divine spirit or will. It derives from the Greek word neuein, meaning 'to nod,' as in "divine approval expressed by a nodding of the head." From this we get the adjective numinous and numinosity. These words suggest that a thing, idea, or event is experienced as if it were a 'divine spirit,' or as the 'presence' of some more-than-human agency, that is 'nodding approval.' That quality infers that a numinous experience gives one the feeling of encountering some 'higher power' or 'creative force' that adds greater significance to an object, thought, or moment in time. There is a suggestion of mystery in such a feeling -- something strange to ordinary experience, palpable yet ineffable, difficult to explain, even 'beyond full comprehension.'
Given that the word sacred gets applied to both overtly spiritual concerns and to more secular ones, we can assume that this numinosity is not exclusively associated with religious contexts. Standing before a magnificent forest, a national flag, or contemplating the founding document of a constitution, one might feel the 'presence' of some 'creative force, a kind of 'will,' something 'alive' -- something sacred. But perhaps even an image, idea, or a concept could trigger such experience.
Sacred Experience versus Sacred Belief: Perhaps, then, this notion of numinous experience is the basis of sacredness. The sensing of some non-human 'will,' some 'creative force' could lead to the designation of places, objects, and concepts as sacred. Subsequently, these things or ideas, such as a statue of a god or a concept of a kind of government, could come to 'stand for' or symbolize the experience of numinosity. In this way, symbols might have the effect of inducing a numinous experience by reminding one of previous such experiences.
However, that raises the likelyhood that the symbols, the representations of a 'sensed divine will' or 'spirit' comes to be regarded as sacred or holy in and of itself. That attitude can be characterized as a belief, meaning an intellectual conception, rather than an immediate felt experience. Here a distinction can be made between sensation induced intuition of 'numinous presence' and a pre-determined belief that a place, object, or idea is sacred. That is, one can feel something which prompts an intuitive sense of sacredness, or one can believe something is sacred, or 'god-like' and of supreme importance, without immediately experiencing numinosity. In the latter case, it would seem that sacredness as numinous experience is reduced to an assumption, a literal truth.
Systems Science and Numinosity: If notions of sacredness do derive from numinous experience, then what could prompt such experience? Is it mere fantasy, a mental projection of human 'will' onto the world, or could it be an intuitive sensing of an actual phenomenon, something demonstrably real? If we seek a description of such a phenomenon through our science, a possible candidate is revealed. The self-organizing, self-directing, thus self-animating activities of complex adaptive systems has been confirmed as factual by systems science. This purposeful, self-regulating, adaptive character of such systems can be understood as 'willful agency.' It is evident not only in animals but in the larger systems of ecologies and human social systems. It is the fundamental 'force' that creates and maintains the biosphere. Similarly, this self-animating agency shapes and directs human social systems as well. Thus a form of government that orders and directs a society could be experienced as numinous.
For people who live in intimate relationship to Nature, like our hunter-gatherer forebears, the interdependent interactions of natural systems pervades their experience. In the absence of a mechanistic worldview, the self-directing agency of these systems becomes 'self-evident.' In that context, it is logical to conclude that 'everything is alive' or 'has spirit.' Moderns term this worldview as "animism." It appears that for archaic humans, numinosity was a common experience, leading to the sense that Nature itself is sacred. As humans came to live in larger scale civilized societies, this sensing of more-than-human spiritual agency became represented in a more theistic manner -- in terms of abstract gods and goddesses that animated both natural and human systems. Thus one could have numinous experience of the presence, the 'nod,' of a god of war, like Ares, or of love, like Aphrodite.
In modern secular societies, few people have any such references for their experience. But it does seem likely people do have some 'sensing' of the agency in systems that science now describes. We still attribute emotion and intention to weather and social systems. We still feel there is something like 'divine will' shaping events. Yet, from the perspective of our mechanistic, materialistic worldview, this cannot be actual. We have no commonly shared category or reference for such 'more-than-animal' agency.
A Science of The Sacred: It now appears that complex systems science has provided a factual basis for numinous experience as 'of system agency.' That provides a new, naturalistic category for 'spiritual agency' as an actual phenomenon that could prompt numinous experience. This means we now have an empirical foundation for understanding sacredness as something real, as the agency or 'will' in systems that makes and shapes the world -- that 'makes things whole' or 'holy,' and thus must not be 'transgressed.' And there is indeed mystery in this naturalistic spiritual impetus. For though science provides factual evidence for it, exactly 'how it does what it does' remains beyond fully analysis and complete explanation.
See Stuart Kaufman's "The Reinvention of The Sacred: A New View of Science, Reason, and Religion" https://www.basicbooks.com/titles/stuart-a-kauffman/reinventing-the-sacred/9780465018888/