Warning This Section Does Contain Spoilers
The Veridical Codex Umbra speaks of the Ritual of Cleromancy.
cleromancy - is a form of sortition, casting of lots, in which an outcome is determined by means that normally would be random, such as the rolling of dice, but are sometimes believed to reveal the will of God, or other supernatural entities.
The Raven uses this Ritual to determine who will be picked as Perfect Vessels. Alexander Thomas was picked as a Perfect Vessel and we are told him mother struggles with this decision. A decision that should, in all reality, elate her. Does this mean that her son was killed? Is she torn in how she feels because she had to lose her son at the hand of The Raven?