Rudolf Steiner: "If here someone is a practical materialist and does not believe in idealism, then he loves existence only. But in order that this conviction of the merely obvious existence may not spread, there continually arise from time to time the Idealists, who lead humanity to believe in ideals and their efficacy, in the power of Idealism in the progress of history. These ideals of the ethical, the beautiful, the religious, are carried into the world. Certainly the absolute materialists will have nothing to do with them; at most they dispose of them in a few words. But just that which in the material sense does not seem to exist, is carried into the physical plane as the most precious thing in life. And if the evolution of humanity on the Earth be considered from a higher human point of view, then one may say: Certainly nature is there, great and significant. But what would this whole human life be if existing nature alone were there, be it ever so beautiful: if man were not capable of having ideals, if he could not be spurred forward, not by that which does not exist, but by that which ought to exist, the ethical, religious, artistic, and educational life. It is the non-existing, we might say, that presses in on us from a spiritual world, as the ideals of humanity — that which does not exist but that ought to exist — that alone makes life valuable. Everyone who is not utterly submerged in the swamp of materialism feels this very strongly. And so those who in the course of history are in a special sense the bringers of ideals appear as those who alone give value to the life of existence, out of that which ought to exist."
Source: http://martyrion.blogspot.com/2018/09/being-and-nothingness.html