That's Meridian. Meridian is one of the two natural forces of this world, and it's Creation and life itself. People with Shards are able to channel that energy for a lot of things, but one of them is to fill the iliachtida with its light.

[ He smiles encouragingly before reaching up to touch his necklace ]

If your soul is compatible with Meridian, you'll Harmonize with it. And from there, you'll find it can always light your way home. Your Meridian will just flow naturally to it.