There is no deed ever done in isolation. Every act is prepared by previous actions which make the deed in question possible, and which in turn make further deeds possible. And while nothing is done in isolation, the deed itself is a free act, sometimes requiring a lot of courage.
Our Gospel today is part of the story of Mary's acceptance of God's will that she should become the mother of the Savior. Mary's action here had been prepared through the message of the prophets and more recently through her own Immaculate Conception and yet, Mary's acceptance itself was a free act, requiring a lot of courage. Elizabeth recognizes this when she says, "Blessed are you for having believed that the promises of the Lord would be fulfilled."
Today we celebrate the feast of Our Lady of Guadalupe. One of the main features of the story of the apparitions at Tepeyac was the acceptance by Juan Diego of Mary's request that he bring her messages to the Bishop of Mexico City that he should build a Church on the site of the appearances. But notice, this was not done in isolation.
“Your tomorrow is created by the choices you make today. Not only your future; also the future of those with whom your life is connected — and indeed, even the future of persons who are not yet born.”