Mary praises God through song for cracking open the heavens and pouring out justice on a world thirsty for it. She points to the power of the Spirit because her Son will relieve the proud and powerful from their self-righteousness, and He will fill the poor with more than money can buy.
And she sings of it already having happened because time is different with God.
The incarnation is not God’s last minute hail Mary to fix the world. It is, was, and always will be God’s decision to dwell with us. In the beginning was the Word and the Word was with God. God was always going to dwell with us because God always dwells with us and God will always dwell with us...