Mary was there. It was by her prayer that the Holy Spirit descended on the Mystical Body and came to abide in it with all his "greatness, power, glory, victory and majesty." (1 Chron 29:11) Mary reproduces in respect of the Mystical Body of Christ every service which she rendered to his actual Body. This law applies to Pentecost, which was a sort of new Epiphany. She is necessary to the one as she had been to the other. And so of all divine things to the end: if Mary is left out, God's Plan is not conformed to, no matter what one's prayers and works and strivings may be.
If Mary is left out, God's Plan is not conformed to
And if Mary is not there, the grace is not given. This is an overpowering thought. It may provoke the question: "Do those who ignore or insult Mary receive no graces?" They do, indeed, receive graces, for failure to acknowledge Mary may be excused on grounds of utter ignorance. But what a sorry title to Heaven! and what a way of treating her who helps us! Moreover, the graces which come in such circumstances are but a fraction of what should flow, so that one's life's work is largely failing.
(The Official Handbook of the Legion of Mary, Chapter 39)