The difficulty, then, is how to arrive at the true knowledge of the most holy Virgin and so find grace in abundance through her. God, as the absolute Master, can give directly what he ordinarily dispenses only through Mary, and it would be rash to deny that he sometimes does so. However, St Thomas assures us that, following the order established by his divine Wisdom, God ordinarily imparts his graces to men through Mary. Therefore, if we wish to go to him, seeking union with him, we must use the same means which he used in coming down from heaven to assume our human nature and to impart his graces to us. That means was a complete dependence on Mary his Mother, which is true devotion to her.
…following the order established by his divine Wisdom, God ordinarily imparts his graces to men through Mary.St. Thomas
From the conclusion of Ch. 2, The Secret of Mary.