But Mary kept all these sayings, pondering them in her heart.
Kept all these sayings, pondering them in her heart ...  Two things of vast importance are here: (1) Mary kept all these sayings.  "In her heart" does not modify "kept," which is an indication that Mary made accurate records of all that took place.  All mothers like to keep a "baby book," and there can be no doubt at all that the most accurate record of things that attended Jesus' conception and birth was made by his virgin mother and, in due course, given to the author of this Gospel.  (2) She pondered them in her heart.  This indicates that Mary continually had these things in mind, meditating upon them, and wondering, perhaps, what the full import of such things could be.