More than one scholar has commented on how strange it is that Apollon, with all that acts upon and all that he has endured in his myths, suffering, exile etc, that he has no apparent mysteries. Nothing like what is enjoyed by his brother Dionysos, to whom Apollon often acts as a slayer. However I am not sure if I agree entirely.
True enough that Apollon, unlike Persephone and Dionysos, does not offer salvation. However I would say he offers liberation. As such his mysteries, such as they are, are entwined with those of Dionysos and Persephone in which he plays the role of liberator in his actions therein as shepherd butcher and harvester. This is his purpose, to bring freedom through destruction, by first encouraging maturation. Just as be cares for the living, he acts for the maturation of the soul. He makes it necessary for the soul to pass through lifetimes before rewarded with dwelling among the blessed. We thus undergo seasons of lean and plentitude, we withstand our purifications, and we understand the role of sucfering that forges who we become.
As such his mystic program, unlike his previously mentioned siblings, does not involve dying. But rather the theme of necessary action, suffering, exile, purification and return. For these reasons little is said about Apollon’s departure occasion, aside from one source stating that a gold statue of Dionysos was erected. The focus not being on the autumn departure, but rather on the spring return.
So we find Apollon in th Orphic hymn playing the springtime Doric melody, as well as a series of festivals occuring before his return that reinacted the steps of his exile. This was important enough to attract pilgrimages to Delphi. Not o ly that but the boy representing Apollon in exile seeking purification was probably awaited in anticipation. I can imagine the solemn hospitality… and then the celebration as he passed through again as the returning god purified! People joyfully following him in procession to Delphi where he arrives with laurel boughs and has a great feast where he holds his brother Dionysos as his guest of honor ( the festival Theoxenia in March).
Spring is the focus. It lacks the autumnal dying mysteries of which he takes part but is not central, and focuses instead on attainment of spiritual freedom attained by the trials of the soul through its own seasons of life and the final victory, as we see the beast within us, accept it, destroy distinction from it, to destroy that which hinders us and ultimately find harmony that will allow us to find peace and freedom.
So even though Apollon has left for his fall retreat I am mindful of this promise, and look forward to setting out his plate on his early spring wanderings at the latter part of Anthesterion, for even tho I feel him more intimately and personally closer, I still look forward to the great occasion of his return.