This short poem from Clark Ashton Smith (CAS) was unpublished in his lifetime, and is not available at The Eldritch Dark, so here's the complete text:
Of one who shares
Even once the Mysteries.
In the Hippocampus Press edition of The Complete Poetry and Translations of Clark Ashton Smith, the editors note that "the Mysteries" refers to the Eleusinian Mysteries of the ancient Greek cult of Demeter and Persephone. The god Dionysus was tangentially involved in those same Mysteries.
The opening phrase "Pagan shadows" feels right in line with the author's general oeuvre, especially if the reader recalls his short fiction set in the (fictional) medieval realm of Averoigne, where pious Christians are routinely undermined and undone by entities from the primeval forests encircling the helpless cathedrals and monasteries.