11 This high office which the Council of Ephesus solemnly declared and sanctioned against the heresy of Nestorius (Cf. Pius XI, Encyclical Lux Veritatis; Acta Apost. Sedis , Vol. 23, P. 493, ss) and greater than which does not seem possible, demands the fullness of Divine grace and a soul immune from stain, since it requires the greatest dignity and sanctity after Christ. Yea indeed, from this sublime office of the Mother of God seem to flow, as it were from a most limpid hidden source, all the privileges and graces with which her soul and life were adorned in such extraordinary manner and measure.
Source: Fulgens Corona (Vatican.va)