Ah. Well. In general, it's to celebrate the longest day of the year. I don't know about how things are in your world, but there's an appreciable difference in daylight between seasons. [She remembers your world sounding different...] And it's also a time to work certain types of magic. Spells tied to summer are strongest at midsummer, after all.

[She pauses, thinking how best to say it.]

As for me, personally...it's my Ascension day. The day I became a god. As a god of summer, it's an important day for me anyway, when my magic is strongest. At home, anyway. But because it's my Ascension as well, it's sort of like a birthday. Not quite, but close.