In celebrating Mary's immaculate heart, we celebrate her single-heartedness. It is sin that divides our heart between self and God, making us no longer single-hearted, no longer immaculate of heart.
But today let us consider another dimension of Mary's heart, a dimension that helps us realize that she is very much in our league, a dimension that is hinted at the end of today's gospel reading, namely, her pondering heart: his mother kept all these things in her heart.
Mary faced a number of situations she did not understand. We are told explicitly this much at the Nativity and in the episode narrated in today's gospel reading. Implicitly we are told the same when she hears Simeon's prediction; when her Son appears to be telling her at the Cana wedding this is none of our business; when she hears Jesus say who is my mother?, and most of all at the foot of the cross. But Mary kept moving on without understanding, pondering in her heart.
Her steadfastness, her single-heartedness was not based on external evidence, but on trust. Mary was assured, even when she could not be sure Being sure and being assured are not the same thing. Being sure speaks of understanding, which rests on evidence. Being assured speaks of an inner stance, which rests on trust.
Lord, I trust You! Let it be done to me as You say!