At the Annunciation, Mary, who was already filled with graces, became, in a very special way, the dwelling place of the Holy Spirit: it was He, in fact, who covered her with his shadow so that she could become, in total adherence to the Word of God, the Mother of the Son of God. Mary is the Ark of the Covenant that carries the Son of God within her (Lk 1:26-38).
The event of Pentecost, described by Luke in the Book of Acts, refers to this amazing experience of listening to the Word of God. Just as the Spirit was present at the forming of the body and soul of the Son of God in Mary, so now the Spirit forms Christ in the nascent Church.
Just as the Spirit moved Mary to go and visit her cousin Elizabeth, so He moves the apostolic mission. And in the same way that He inspires a song of thanksgiving to spring from Mary's heart (Lk 1:46-56), so He is the source of the wonder-filled public witness of the apostles and disciples (Acts 2:4-13).
M. J. Le Guillou - Les témoins sont parmi nous (The Witnesses are in our midst)
Edition Parole et Silence 2004