What is the importance of the "dowry box" in the novel, Fairest of All: A Tale of the Wicked Queen?

The Dowry Box is where the King keeps all of his first wife's letters to Snow White. When he marries the Queen, he entrusts her with the box knowing how important family ties are to his new wife. When the Queen descends into madness, she gives the Huntsman the dowry box telling him to bring back Snow White's heart in it.