"The Lord is magnified, not because the human voice can add anything to God but because he is magnified within us. Christ is the image of God, and if the soul does what is right and holy, it magnifies that image of God, in whose likeness it was created and, in magnifying the image of God, the soul has a share in its greatness and is exalted."
I've been praying the Magnificat for decades, but have never much reflected upon the meaning of this phrase until I read today's second reading in the Office of Readings by St. Ambrose. What does it mean for our soul to magnify the Lord? To magnify means to make so as to look larger. We make the Image of God larger in us by being and becoming holy. It is our actions, not merely saying "Praise God!" If your life doesn't correspond to your knowledge and your words, it does no good.
I think one of the temptations of the Charismatic Renewal was to equate "magnifying" the Lord with saying "Praise God!" or with speaking in tongues.