What is the significance of Mary treasuring and pondering in her heart? In "the Christmas parts" in Luke Mary's reaction to many great occurrences is to treasure and ponder them in her heart.

Is there specific significance to this phrasing or is it simply to highlight Mary's humility?
I suppose Luke got his information from Mary, and for her to have given them as though quoting them after many years proved she pondered and cherished those words, and was watching out for their fulfilment.