Con esso la Madre di Dio inaugurò, quasi direi, l’opera della Redenzione, anticipò l’annuncio del Vangelo, proclamandone il tema, compendiandone la sapienza, profetandone gli effetti infallibili e meravigliosi a beneficio del genere umano.
With this incomparable song the mother of God may be said to have inaugurated the work of Redemption, and anticipated the promulgation of the Gospel by announcing its subject, epitomising its wisdom, and predicting its infallible and marvellous effects for the weal of mankind.
Among Bl. Antonio Rosmini's works is a short commentary on the Magnificat, which is a rather interesting work:
Italian: https://www.rosmini.it/Objects/Pagina.asp?ID=295 (PDF)
After an introduction, he divides the song into two parts. In the first part, the Virgin shows her awareness of what God has done, magnifying the Lord in soul (animal life) and in spirit (mind and will); as part of her pregnancy, she feels the greatness of God's work in her body, and she exults in it by her mind. Thus in a song about the child in her womb, she praises God as Savior, as her ancestor David had done, and that by her bearing the child, she is God's handmaiden in his work of salvation, for which reason she will be called blessed.
This opens the second part of the Magnificat, in which Mary sings as la Regina dei Profeti, the Queen of the Prophets, summarizing the effects of what God is accomplishing. All generations will call her blessed, a prophecy that has already been fulfilled, and, since faith and divine charity alone merits blessedness, that also shows her sanctity and dignity. However, she explicitly attributes this dignity to God; she has it not of herself but because God has done what is great in her. And in describing this work, she highlights that it is a work with three aspects. God has done this specifically as the Mighty One, as divinely omnipotent, and thus the work itself is such as to be appropriate to omnipotence, and her blessedness in proportion to that work. In this way, the Virgin speaks of a greatness beyond any mortal greatness, and a blessedness beyond even ordinary blessedness, but does so in complete humility. But God also performs the work as the one whose name is Holy. The angel, of course, had told her that the Holy that would be born of her would be the Son of God. Thus it is a work expressing the sanctity of God. And the third aspect is that it is a work expressive of the boundlessness of God's mercy, which is given to those who revere Him, from generation to generation.
Nor does she stop at summarizing what God has done in the Incarnation itself; she continues by singing of what God's mercy will do from generation to generation through it. "He has showed the might of His Arm" serves as the compendium of what follows, because "the Arm of God means the Son of God; because the Son springs from the Father as the arm from the body." It is, in other words, an allusion to Isaiah 5:9-11:
Arise, arise, put on strength, O thou arm of the Lord, arise as in the days of old, in the ancient generations. Hast not thou struck the proud one, and wounded the dragon? Hast not thou dried up the sea, the water of the mighty deep, who madest the depth of the sea a way, that the delivered might pass over? And now they that are redeemed by the Lord, shall return, and shall come into Sion singing praises, and joy everlasting shall be upon their heads, they shall obtain joy and gladness, sorrow and mourning shall flee away.
What Isaiah prophesied is now being fulfilled: the Arm of the Lord has put on strength, and will wound the Dragon that the delivered might pass over the mighty deep and the redeemed might come with everlasting joy to Zion.
Three serious evils infect the unredeemed world, and the Virgin now goes on to prophesy that the Lord will undo them:
(1) la superbia dei falsi sapienti, the pride of false sages
(2) la prepotenza dei forti, the tyranny of the mighty
(3) la dissolutezza dei ricchi, the dissoluteness of the rich
The Arm of the Lord will scatter the proud in the conceit of their hearts, the foolishness of God overcoming the wisdom of the world; He will cast the mighty from their thrones, exalting the humble by the preaching of His Church; and He will send the wealthy away and by the charitable work of His disciples fill the hungry.
In expounding this, Mary is also anticipating the teaching of her Son. (Rosmini mentions the Beatitudes in the Sermon on the Mount in Matthew in particular, but I think his point is even stronger if one looks at the corresponding passage in Luke 6, which we often today call the Sermon on the Plain, since it is inevitable in reading Luke to see it as calling back to the Magnificat: Blessed are the poor, for you shall receive the kingdom of God; blessed are the hungry, for you shall be filled; blessed are you who weep, for you shall laugh; blessed are you when you are hated, for your reward in heaven will be great. But woe to the rich, woe to the filled, and so forth.) The Holy Virgin is thus given the honor of being the first to proclaim the Lord's own teaching.
Christ, the Virgin Mary prophesies, will overcome the philosophers of the day, the imperial and royal powers, the wealthy; He shall do so by a wisdom that goes beyond the counsels of the human heart, by humility, and by satisfying the hunger of those in need. But the prophecy of the Virgin extends beyond us, for there is another thing that she attributes to the Arm of God: mercifully lifting up Israel from the ground as He had promised Abraham and Abraham's descendants since. Thus she affirms that God's promises to Israel are everlasting.
"In this Canticle, then," says Rosmini, "which is at once so simple and sublime, the predictions of the ancient prophets are summed up, the history of the Church is epitomised, the pith of gospel wisdom is concentrated, and the wonders of its infallible results are narrated." In a single panorama we find captured the whole Christian view of all of salvation history.