What is the radical or root point on which Heidegger’s philosophical relevance turns? It seems to me this:
The history of Western philosophy, science, and technology, rooted in Greek thinking, have taught Western civilization always to think of “being” as some particular kind of “substance”. Substance traditionally refers to what ultimately underlies the appearance of things: the underlying kind of thing or a kind of “stuff” arranged in a particular way.
One can see in our contemporary culture a continuing debate over whether to think of true “being” as either a ‘material’ or a ‘spiritual’ sort of ‘stuff’. Does “being” ultimately refer to some kind of ‘material stuff’, e.g., particles, atoms, or energy? Or does “being” refer instead ultimately to some kind of ‘mental stuff’, e.g., gods, minds, or will? If being is one of these kinds of things, then how is it essentially arranged or structured?
Heidegger’s radical innovation in philosophy is to see that these very questions are malformed, and so thus are the answers.
The preceding questions are for Heidegger examples of metaphysics done poorly: ways of thinking suffering from a conceptual form of ‘substance abuse’, so to speak. Our inclination to understand “being” in terms of a substance, some sort of stuff, signifies a way of life in which we presuppose an imperative to render all beings into forms — whether a physical or mental form — that will be utilizable or serviceable to technical control in some way.
In contrast, Heidegger argues that this way of thinking covers-over and obscures the primordially temporal character of the “being” of beings, whereby “being” always refers to the event of a being. This insight does not deny the utility of concepts and the scientific representation of beings, it only denies them ultimate truth for obscuring the primordial event-structure whereby beings are revealed in their being by the language-bearing being-there who temporally reveals them.
For Heidegger, the history of Western philosophy and science have obscured the primordial truth that “being” always refers to an event thoroughly characterized by a temporal disclosure. What we ourselves are, in the most authentic sense, is a stretching and pointing of time between a birth and a death, beings in time that are timely.
It follows from this that the meaning of “being” is always shaped by a particular temporal horizon of possibilities.
For example, our age, our time collectively, is an age of technology. This explains why it is that we tend to interpret the “being” of all beings in terms of possibilities for technological manipulations.