Over the last few days Mace has trudged through dusty-tomes and notes, everything that she could get her hands on in regards to Souls, specifically Awakened Souls. She finds a great little but, she has a few scant leads. The Awakened Soul, and Souls in general, is the jewel of life. For the Awakened, it is the soul that discovers the Supernal and it is the Soul, a Magi can learn to travel within.
Perhaps, it is the Soul that contains the Promethean Fire that is the Spark of Life as they know it.
What Mace realizes, is that some Magi understand the power inherent in the Soul and create Soul Stones from their own – a vaguely gray area but largely accepted. She also makes the logical conclusion that some Magi have, in their hubris, sought to steal it from others. What they can do with it, is up to Mace to theorize.