[NOTE: In the quotation below, the original German word that I have translated into English as mental-picturing is "Vorstellung." This German word is often rendered in English as "idea" or "representation." However, the literal meaning of the German is before-placing, in the sense of placing before the mind's eye; thus, "Vorstellung" basically refers to the mental act of placing something before the "eye" of inner vision. In other words, the German expression "Vorstellung" refers to anything that happens in the mind, or is inwardly present to the mind. It includes all states consciousness, all contents of consciousness, both concrete pictures and abstract concepts. - Pastor Vin]

"The world is my mental-picturing." This is a truth that holds good for everything that lives and perceives, although only the human being can bring this fact into reflective and abstract consciousness. Moreover, it is only by attainment of this insight that genuine philosophical wisdom finally dawns on a person. It then becomes clear and certain to a person that what he knows is not a sun and an earth, but only an eye that sees a sun, a hand that feels an earth; that the world which surrounds each person exists only as mental-picturing, in other words, only in relation to something else, namely consciousness, which is the very person, or self. If any truth can be stated as something self-evident, it is this. For it is the expression of the most general form of all possible and thinkable experience, a form which is more general than time, or space, or causality, for they all presuppose it. . . . No truth, therefore, is more certain -- more independent of all others, and less in need of proof -- than this, that all that exists for knowledge, and therefore this whole world, is only object in relation to subject, perception of a perceiver, in a word, mental-picturing. This is obviously true of the past and future, as well as of the present, of what is farthest off and of what is near; for it is true of time and space themselves, and all these distinctions arise only within time and space. All that in any way belongs to the world -- or can belong to the world -- is therefore inevitably dependent on the subject, and exists only for the subject. "The world is mental-picturing." This truth is by no means new. It was implicitly involved in the sceptical reflections which were the starting-point of Descartes. However, Berkeley was the first person who distinctly enunciated it, and by this he has rendered a permanent service to philosophy, even though the rest of his teaching should not endure. . . . By contrast, just how early again this truth was recognised by the wise men of India -- appearing indeed as the fundamental tenet of the Vedauta philosophy ascribed to Vyasa -- is pointed out by Sir William Jones in the last of his essays, "On the Philosophy of the Asiatics" (Asiatic Researches, vol. iv., p. 164). In this essay, he states that, "The fundamental tenet of the Vedanta school did not consist in denying the existence of matter, that is, of solidity, impenetrability, and extended figure (to deny which would be lunacy), but rather in correcting the popular belief about it, and in contending that it has no existence independent of mental perception; in other words, that existence and perceptibility are interchangeable terms."

That which perceives all things and is itself not a perception is the subject. Thus, it is the supporter of the world, i.e., the necessary condition of all phenomena and objects; it is always pre-supposed by all of our experiences; for everything that exists, exists only for the subject. Each person finds that he himself is this subject, yet only in so far as he perceives, not in so far as he is an object of perception.

But his body is object, and therefore from this point of view we call it mental-picturing. For the body is an object among objects, and is subject to the laws of objects, although it is an immediate object. Like all objects of perception, it lies within the universal forms of knowledge,that is, time and space, . . .. The subject, on the contrary, which is always the perceiver -- never the perception -- does not come under these forms of time and space, but rather time and space themselves presuppose this subject. . . . We never perceive this subject, but it is always the perceiver wherever there is perceiving.

So then, the world as mental-picturing . . . . has two fundamental, necessary, and inseparable halves. The one half is the object, the forms of which are space and time, and through these multiplicity. The other half is the subject, which is not in space and time. For this subject is present -- entire and undivided -- in every percipient being. So that any one percipient being, with the object, constitutes the whole world as mental-picturing, just as fully as the existing millions could do. But if this one were to disappear, then the whole world as mentally-picturing would cease to be. These two halves are therefore inseparable even for thought, for each of the two has meaning and existence only through and for the other. Each appears with the other, and vanishes with it. They limit each other immediately. Where the object begins the subject ends.
(The World as Will and Idea, Arthur Schopenhauer)

"An essential part of projecting one's life into supersensible worlds consists in the fact that beings take the place of the conditions and qualities which the consciousness has around it in the physical world." (A Way to Human Self-Knowledge & The Threshhold of the Spiritual World, Rudolf Steiner)

"When clairvoyant consciousness enters this spiritual world of living thought-beings, it feels itself to be in a completely new relationship towards the physical world. The latter confronts it in the spiritual world as another world, just as in the physical world the spiritual world appears as another one. But to spiritual sight the physical world has lost everything which can be perceived of it within physical existence. All those qualities seem to have vanished which are grasped with the senses, or the intellect which is bound up with the senses. On the other hand, it is obvious from the standpoint of the spiritual world that the true, original nature of the physical world is itself spiritual To the soul's gaze, looking from the spiritual world, there appear instead of the previous physical world, spiritual beings unfolding their activities in such a way that through the converging of those activities that world comes into being which, looked at through the senses, is the very world that man has before him in his own physical existence. Seen from the spiritual world, the qualities, forces, materials, etc., of the physical world disappear as such, and are revealed as mere appearances. From the spiritual world man sees only beings, and in them lies true reality." (A Way to Human Self-Knowledge & The Threshhold of the Spiritual World, Rudolf Steiner)