[Dunya] remembered, to her grief, the girl who had come to Ivan Kalita’s halls, lost and frail and achingly beautiful, trailing miracles behind her … perhaps she had found peace with him, at least for a little. But … little by little that fiery glow, the light to take one’s breath, had faded. Dunya had mourned her passing long before they put her in the ground.”
-- Narration (Part 1, Chapter 2)

Importance: Dunya remembers her beloved Marina, who died shortly after giving birth to protagonist Vasya. There are hints here of Marina's otherworldly nature, hints that simultaneously serve as foreshadowing for similar aspects of otherworldliness in Vasya.

Such a look the Grand Prince gave me, Father,” [Sasha] said. ‘As though he knew my thoughts better than I do.’ ‘They are all like that, the princes that live,’ said Pyotr … ‘They all have too many brothers, and all are eager for the next city, the richer prize...
-- Sasha / Pyotr (Part 2, Chapter 4)