One of the images of Mary is that of a window. One does not look at a window, one looks though it at something else. Mary is a window through which we look to see her Son. Another image of Mary is that of the moon. The moon is a cold rock. But when the sun hits it, it gives a glorious brilliance for us to see on earth on a dark night. So Mary’s brilliance is in that she reflects her Son to us. “My soul magnifies the Lord.”
In the same way this next paragraph (66) of Lumen Gentium states it, William Wadsworth once said more poetically is that Our Lady is “our tainted nature’s solitary boast.” She is our exemplar par excellence. Where Jesus is a divine person, Mary is fully human and so is set at our head to lead us in the way of fully following her Son. Such has been the case since the very inception of the Church. This is attested to in Luke where Mary says, “All generation shall call me blessed.”
A devotion to Mary is essentially different from the devotion given to the Trinity. A devotion to the Father, Son, and Holy Spirit is an end unto itself. The buck stops there so to speak. God is the object of all true worship. Devotion to Mary is a pathway to a deeper understanding and love of the Trinity.
Think of it this way: You might have a particular devotion to a preacher that simply wows you. You might follow this person around, attend many services, and listen to numerous recordings of sermons and teachings. But if the person’s preaching only leads you to like that person more deeply, that person has failed. The inspirational talks are supposed to be a pathway to heaven and entice you further up that glorious trail. True and loving devotion to Mary is to do the same thing.