Whenever Frank Duff spoke and priests were present he would invariably begin by acknowledging their presence and thanking them. This was not just a polite formality or a form of obsequiousness but the expression of a profound reverence for the priesthood deeply rooted in his faith and theological reflection.

He saw his own vocation as a layperson and the innermost reality of the Legion of Mary as intrinsically and therefore inseparably related to the vocation of the priest. And, vice versa, he saw the vocation of the priest, although different in kind, as essentially related to the vocation of the laity. Together he saw them as the divinely planned way of the most authentic and effective evangelisation.