7 And that through the Virgin, and through her more than through any other means, we have offered us a way of reaching the knowledge of Jesus Christ, cannot be doubted when it is remembered that with her alone of all others Jesus was for thirty years united, as a son is usually united with a mother, in the closest ties of intimacy and domestic life. Who could better than His Mother have an open knowledge of the admirable mysteries of the birth and childhood of Christ, and above all of the mystery of the Incarnation, which is the beginning and the foundation of faith? Mary not only preserved and meditated on the events of Bethlehem and the facts which took place in Jerusalem in the Temple of the Lord, but sharing as she did the thoughts and the secret wishes of Christ she may be said to have lived the very life of her Son. Hence nobody ever knew Christ so profoundly as she did, and nobody can ever be more competent as a guide and teacher of the knowledge of Christ.
Source: Ad Diem Illum Laetissimum (Vatican.va)