I'm surprised at Moose's answer. WE see this big glyph more than once.

The second time is here:



After you fight Ifrit.

We don't have an explanation as to why the crystal collection, but didn't FFIII heros need to collect crystals to get to the World of Darkness and fight the Warriors of Dark? The glyph in FFIII is the portal to the "World of Darkness" I was wondering if it is something similar here.