The essence of art for Heidegger is projection. Art projects being.
Now project has two meanings. A project (noun) is a structured effort to do something, to make something. Designing is a project: deliberately setting out on a sequence of actions that will result something new in the world.
However, project (verb) means to amplify something, to make it bigger, to throw the light through it onto a screen so that it can more easily be seen. Projecting draws attention to something that already exists; it makes that thing shine, revealing its many aspects. In a way, this is like visual communication design: taking an existing message and recasting it so that its meaning becomes clearer or more powerful or more incisive.
So art is a project of projecting. It is a project that makes things that in turn remake our world, opening up aspects of the world that we hadn’t noticed. But contrary to usual conceptions of artists as special people who can create something totally new, Heidegger is insistent that art also be understood as projecting, as taking something already lying there, and drawing attention to it or looking at it anew. The artist is not the one and only origin of a work of art. The world itself (or more properly, the earth, rising up into the world in particular ways) is also a major aspect of the origin of a work of art. The artist can only make use of ways in which the world (or earth) is already making itself apparent.
Another way to make sense of this is to understand why Heidegger makes poetry the model for all other kinds of art. On the one hand, Heidegger makes use of the word poetry because it derives from the Ancient Greek word for making: poiesis. So according the Greeks, poetry is the primary way of understanding making. But poetry is nothing but the attempt to articulate things, to manipulate a finite set of words to make them reveal something new. Poems are made up of words that we have to know the meaning of; but by assembling them in particular ways, new ways of understanding those meanings emerge; and so too do new ways of understanding the world. The world is remade by being rearticulated.
This is a particularly important aspect of Heidegger’s thinking: it is what gets called ‘the middle voice.’ This is a grammatical term referring to things that happen that are not active (‘I made a work of art’) nor passive (‘a work of art was made’), but somewhere in between (‘I could feel a work of art arising as I was making’). To some extent, the point of the OWA essay, is to draw attention to the many (circular) origins behind any art work.
But do notice that Heidegger in this essay is focusing more on the active side than the passive side. Early and late in his thinking, he was more focused on the passive side, on Gelassenheit which means releasement, going with the flow as it were. In this essay (and particularly in earlier versions of it, Heidegger was focused more on the founding and instituting that artworks do, almost at a historical scale. What artworks project, even if via a middle-voiced poetic process, is something that can (and in this essay, should, Heidegger suggests) become a project for a whole nation of people, clarifying for them their nature, history and destiny.
This seems to me more appropriate to understanding the role of ‘design’ in relation to OWA. Designers are more forceful in their projects and projections. They are not sole creators; they still must make use of the what the world offers them, in terms of materials, technologies and the patterns of everyday life of this or that target market. But, having worked insightfully with often unnoticed aspects of the ways of the world, designers can do history-making things, like enabling major shifts to how we transport ourselves, or communicate amongst ourselves, or dress ourselves, etc.