“All profound world-view is mysticism, the essence of which is just this: that out of my unsophisticated and naïve existence in the world there comes, as a result of thought about self and the world, spiritual self-devotion to the mysterious infinite Will which is continuously manifested in the universe.”

Thoughts and Glimpses (1916-17)

Source: Who Is Man? (1965), Ch. 5<!-- The sense of the ineffable, p. 88 -->
Context: Our concern with environment cannot be reduced to what can be used, to what can be grasped. Environment includes not only the inkstand and the blotting paper, but also the impenetrable stillness in the air, the stars, the clouds, the quiet passing of time, the wonder of my own being. I am an end as well as a means, and so is the world: an end as well as a means. My view of the world and my understanding of the self determine each other. The complete manipulation of the world results in the complete instrumentalization of the self.

31
The Zürau Aphorisms (1917 - 1918)

Kulturphilosophie (1923), Vol. 2 : Civilization and Ethics
Context: Affirmation of the world, which means affirmation of the will-to-live that manifests itself around me, is only possible if I devote myself to other life. From an inner necessity, I exert myself in producing values and practising ethics in the world and on the world even though I do not understand the meaning of the world. For in world- and life-affirmation and in ethics I carry out the will of the universal will-to-live which reveals itself in me. I live my life in God, in the mysterious divine personality which I do not know as such in the world, but only experience as mysterious Will within myself.
Rational thinking which is free from assumptions ends therefore in mysticism. To relate oneself in the spirit of reverence for life to the multiform manifestations of the will-to-live which together constitute the world is ethical mysticism. All profound world-view is mysticism, the essence of which is just this: that out of my unsophisticated and naïve existence in the world there comes, as a result of thought about self and the world, spiritual self-devotion to the mysterious infinite Will which is continuously manifested in the universe.

Source: The Doors of Perception & Heaven and Hell

Source: Hogfather

On Truth and Lie in an Extra-Moral Sense (1873)
Context: The drive toward the formation of metaphors is the fundamental human drive, which one cannot for a single instant dispense with in thought, for one would thereby dispense with man himself. This drive is not truly vanquished and scarcely subdued by the fact that a regular and rigid new world is constructed as its prison from its own ephemeral products, the concepts. It seeks a new realm and another channel for its activity, and it finds this in myth and in art generally. This drive continually confuses the conceptual categories and cells by bringing forward new transferences, metaphors, and metonymies. It continually manifests an ardent desire to refashion the world which presents itself to waking man, so that it will be as colorful, irregular, lacking in results and coherence, charming, and eternally new as the world of dreams. Indeed, it is only by means of the rigid and regular web of concepts that the waking man clearly sees that he is awake; and it is precisely because of this that he sometimes thinks that he must be dreaming when this web of concepts is torn by art.