Devotion, as St. Thomas teaches, consists in the readiness with which our will conforms itself to the will of God. This was the principal virtue which rendered his most Holy Mother so dear to God. This also was the signification of the answer which our Lord gave to the woman who called the womb which bore him blessed:
Yea rather, blessed are they that hear the word of God and keep it. By this, according to Venerable Bede, our Lord meant that Mary was more blessed by the union of her will with that of God than by being his Mother. That flower which always turns towards the sun is a real type of Mary. The divine will was alone the aim and satisfaction of the heart of Mary; as she herself proclaimed, My spirit hath rejoiced in God my Saviour.
O blessed art thou my Lady, who wast always, and in all, united to the divine will. Obtain for me the grace to spend the rest of my life in constant conformity to the will of God.
From The Glories of Mary by St. Alphonsus de Liguori