The following is from a new edition of a book by Martyn Lloyd-Jones, Magnify The Lord, which is based entirely on Luke 1:46-55. This arrives just in time for Christmas and Advent meditations.
…Why is Mary magnifying the Lord? Why does her spirit exult in God her Savior? She really surprises us with the answer. It is not primarily because of what has happened to her. She does not mention that: it comes in but that is merely an incident in her hymn of praise. So what is the cause of her adoration, of her praise? It is because God himself is who and what he is, and because of what he is doing with respect to the world.
Mary’s eye, in other words, is not upon herself. You see how certain parts of the Church have so abused and made an utter travesty of this. Mary is full of humility. She refers to herself as what she is — ‘the low estate of thine handmaiden.’ There is nothing here about the ‘mother of God’ and about ‘the queen of heaven.’ Mary is not thinking about herself. Mary has seen something that makes her forget about herself and this is the ultimate test of a true understanding of what happened when God in the fullness of times ‘sent forth his Son made of a woman, made under the law’ (Gal. 4:4).
Mary is rejoicing not so much in the fact that she is to be given this great privilege, she has been reminded by Elizabeth of what this is and of how people are going to caller her blessed, and she repeats that, ‘from henceforth all generations shall call me blessed.’
But that is not the thing that really moves her. It is what God is doing: this historic event, this climactic action of God himself. She is humbled and grateful at the thought of the fact that she is to be given a part and a place in this, but it is the thing itself that moves her and makes her sing and worship.
She is filled with a sense of amazement, of worship, adoration, and utter astonishment. She sees the inner meaning of the action. She has a glimpse and a glimmering of understanding of the whole purpose of salvation, what God is doing in bringing forth his Son into the world, even out of her womb.
Now that is the secret of this song. And it is also the secret of the whole Christian position. What is it that leads to worship and to praise, to exultation, to adoration? And the answer is that it is always the understanding.
The only singing that is of any value in the sight of God is that which is based upon the understanding, the understanding of the truth…
Magnify the Lord, pp. 19-20