From: Luke 11:27-28
Responding to the Word of God
 As He (Jesus) said this, a woman in the crowd raised her voice and said to Him, "Blessed is the womb that bore You, and the breasts that You sucked!"  But He said, "Blessed rather are those who hear the word of God and keep it!"
27-28. These words proclaim and praise the Blessed Virgin's basic attitude of soul. As the Second Vatican Council explains: "In the course of her Son's preaching she [Mary] received the words whereby, in extolling a Kingdom beyond the concerns and ties of flesh and blood, He declared blessed those who heard and kept the word of God (cf. Mark 3:35; Luke 11:27-28) as she was faithfully doing (cf. Luke 2:19_51)" ("Lumen Gentium", 58). Therefore, by replying in this way Jesus is not rejecting the warm praise this good lady renders His Mother; He accepts it and goes further, explaining that Mary is blessed particularly because she has been good and faithful in putting the word of God into practice. "It was a complement to His Mother on her "fiat", `be it done' (Luke 1:38). She lived it sincerely, unstintingly, fulfilling its every consequence, but never amid fanfare, rather in the hidden and silent sacrifice of each day" ([St] J. Escriva, "Christ Is Passing By", 177). See the note on Luke 1:34-38.
[Note on Luke 1:34-38 states:
34-38. Commenting on this passage John Paul II said: "`Virgo fidelis', the faithful Virgin. What does this faithfulness of Mary mean? What are the dimensions of this faithfulness? The first dimension is called search. Mary was faithful first of all when she began, lovingly, to seek the deep sense of God's plan in her and for the world. `Quomodo fiet?' How shall this be?, she asked the Angel of the Annunciation [...]."
"The second dimension of faithfulness is called reception, acceptance. The `quomodo fiet?' is changed, on Mary's lips, to a `fiat': Let it be done, I am ready, I accept. This is the crucial moment of faithfulness, the moment in which man perceives that he will never completely understand the `how': that there are in God's plan more areas of mystery than of clarity; that is, however he may try, he will never succeed in understanding it completely [...]."
"The third dimension of faithfulness is consistency to live in accordance with what one believes; to adapt one's own life to the object of one's adherence. To accept misunderstanding, persecutions, rather than a break between what one practises and what one believes: this is consistency [...]."
"But all faithfulness must pass the most exacting test, that of duration. Therefore, the fourth dimension of faithfulness is constancy. It is easy to be consistent for a day or two. It is difficult and important to be consistent for one's whole life. It is easy to be consistent in the hour of enthusiasm, it is difficult to be so in the hour of tribulation. And only a consistency that lasts throughout the whole life can be called faithfulness. Mary's `fiat' in the Annunciation finds its fullness in the silent `fiat' that she repeats at the foot of the Cross" ("Homily in Mexico City Cathedral", 26 January 1979).]
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.