So, why does Heidegger give such pride of place to Meyer's poem? The answer to this puzzle (which too few readers even notice) is that the poem introduces the broader philosophical context of Heidegger's project by conveying his emerging understanding of historicity and epochality, the doctrines according to which, respectively, our fundamental sense of reality (1) changes over time and (2) takes the shape of a series of unified constellations of intelligibility. For, the ontological “truth” that Meyer's poem embodies—and “sets to work,” in Heidegger's creative appropriation of the poem—is that truth itself is essentially historical and, moreover, that this essential history of truth forms three successive “epochs,” in the same way that the “jet” of water fills the three consecutive “basins” in Meyer's poetic fountain. For Heidegger, to put it more precisely, the relations Meyer's poem describes between the fountain's original “jet” and its three successive water basins illuminate the relations between “being” itself (that is, as we will see, the inexhaustible ontological source of historical intelligibility) and the three main historical “epochs” or ages in Western humanity's understanding of being (as Heidegger conceived of this “history of being” in 1936), namely, ancient “Greece,” “the middle ages,” and “the modern age”.
Thus, for example, just as the original “jet” of water “falls” into the fountain's successive basins, so the “overflowing” ontological riches concealed in the ancient world were first diminished in the medieval world. “The Origin of the Work of Art” make the contentious case that this ontological diminution “begins” when concepts central to the ancient Greek understanding of being get translated into Latin without a full experience of what those concepts originally revealed. Hence the obvious appeal for Heidegger of Meyer's suggestive line: “Veiling itself, this [first basin] overflows / Into a second basin's ground”. What remained of these ontological “riches” in the medieval world was then transposed into and reduced further in the modern epoch which, like the fountain's third basin, stands at the furthest remove from its original source. It thus seems clear that Heidegger included Meyer's poem because he believed it suggestively illuminated the way the history of being unfolds as a history of decline, a “fall” which results from this history's increasing forgetting of the source from which it ultimately springs—the Ur-sprung or “origin” of Heidegger's essay's title—in a word: “Being” (Sein), Heidegger's famous name for the source from which all historical intelligibility originates (by way of the disclosive “naming-into-being” which Heidegger understands as the “poetic” essence of art).