Read "A Precept" at The Eldritch Dark:
This is a wonderful artistic manifesto from Clark Ashton Smith (CAS). The closing quatrain is a thing of beauty, and could serve as a complete poem all by itself:
No shining words of stone—
Shadow and cloud alone—
These shall the poet seek eternally,
Whose lines would carve the mask of Mystery.
In a mere twelve lines, CAS has managed to capture the essence of his poetic craft, and has articulated the raison d'être of that craft.