The Annunciation and Pentecost are “experiences of listening to the Word of God in the Spirit”

At the Annunciation, Mary, already filled with graces, becomes in a very special way the dwelling place of the Holy Spirit: it is He, in fact, who covers her with his shadow so that she becomes, in total adherence to the Word of God, the Mother of the Son of God. She is the Ark of the Covenant, bearing the Son of God within her (Lk 1:26-38). 

The experience of Pentecost, as described by Luke in the Book of Acts, refers back to this exemplary experience of listening to the Word of God in the Spirit, at the Annunciation. 

Just as the Spirit formed the body and soul of the Son of God in Mary, so the Spirit forms Christ in the nascent Church. Just as the Spirit gave the impetus to Mary's visit to her cousin Elizabeth, so the Spirit gives rise to the apostolic mission. And just as Mary's heart burst forth in a song of thanksgiving (Lk 1:46-56), so it is the source of the amazed witness of the apostles and disciples (Acts 2:4-13).

M. J. Le Guillou, Les témoins sont parmi nous , Edition Parole et Silence 2004