The redemption of the world, in its fullness, happens through the Son of God, whose incarnation requires the human participation of Mary.
Mary did not know that she had been conceived in preparation for being the mother of Jesus Christ. When the angel announced that she would give birth to the Son of God, she did not understand and, troubled, she questioned how this could be. The angel replied: “The Spirit will come upon you”. The Spirit in the angel’s response is the same one that hovered over the waters in the beginning in Genesis 1:2, and renews the face of the ground in Psalm 104:30:
“Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters.”
Genesis 1:2
“When you send your Spirit, […] you renew the face of the ground.”
Psalm 104:30
It is because of her own faith and hope, and her memory of passages like these, that Mary responded: “Behold, I am the handmaid of the Lord; let it be done to me according to his word” (Lk 1:38).
Mary is the epitome of divine intervention in humanity, and how God’s intervention depends on a human response. It is Mary’s human capacity to respond “Yes” to the Word of God that makes her a helper of God in the salvific action of humanity.