41 In order to understand better this sublime dignity of the Mother of God over all creatures let us recall that the holy Mother of God was, at the very moment of her Immaculate Conception, so filled with grace as to surpass the grace of all the Saints. Wherefore, as Our Predecessor of happy memory, Pius IX wrote, God "showered her with heavenly gifts and graces from the treasury of His divinity so far beyond what He gave to all the angels and saints that she was ever free from the least stain of sin; she is so beautiful and perfect, and possesses such fullness of innocence and holiness, that under God a greater could not be dreamed, and only God can comprehend the marvel."
Source: Ad Caeli Reginam (Vatican.va)