A vocation invites the newness of responding to all the present which is offered to us. Fr. Giussani gives the example of Mary who, immediately after the Annunciation, doesn't sit around and worry about what to do next, but gets up to go to Elizabeth as she has just heard from the angel that her elder cousin was expecting a baby. She wasn't ordered to do so, but we often wait around for messages instead of listening to the gentle promptings of the heart. No big announcements were made about her news; she just went about her life, following the subtlety of invitation in her own circumstances with perfect attentiveness and letting the predicament of her situation be worked out in the peace of God.
The design of God is absolutely beyond us, always; it cannot be narrowed or imprisoned within the limits of our imagination. But one who is always willing to change everything according to what God wants–and mark these words, what God wants through the circumstances, because, for Our Lady, three minutes, a minute before, it wasn’t even imaginable that the Annunciation could happen–circumstances, especially those that vex us the most, that are inevitable circumstances, these are precisely the ones that mark the road of God; the person who is open to this is not attached to anything of his own, and he’s free. So the first consequence is that he is attentive, extremely attentive to the needs of others. In fact, as soon as the Angel left, Our Lady decided right away, a girl of fourteen or fifteen years, to travel that very long journey–one that when you go to Palestine you usually do by bus or by car–of over 60 miles in the midst of that stony land, to go visit her cousin Elizabeth, because the Angel had told her that she was six months along with the child in her womb. The first thing she did was to share the need and the toil of her cousin Elizabeth, at very great sacrifice. When are you free? You’re free when you’re willing to do what God wants. Before the Infinite, only before the Infinite is man free, detached from himself. When you’re like this, you’re immediately ready to feel and meet the needs of others. What a lesson for us! These are the first characteristics of a man who lives life as a pilgrimage. (Giussani, "Mary: Faith and Faithfulness"