Someone might think that it was easy for the Virgin Mary to believe, living as she did in daily contact with Jesus. In this regard, however, we must remember that the unique aspects of her Son's personality were usually hidden; even if his way of acting was exemplary, he lived a life similar to that of his peers.
During his 30 years of life in Nazareth, Jesus did not reveal his supernatural qualities and worked no miracles. At the first extraordinary manifestations of his personality, associated with the beginning of his preaching, his relatives (called "brothers" in the Gospel), assume—according to one interpretation—responsibility for taking him home, because they feel his behavior is not normal (cf. Mk 3:21).
In the dignified and hard-working atmosphere of Nazareth, Mary strove to understand the workings of Providence in her Son's mission. A subject of particular reflection for his Mother, in this regard, was certainly the statement Jesus made in the temple of Jerusalem when he was 12 years old: "Did you not know that I must be in my Father's house?" (Lk 2:49). Meditating on this, Mary could better understand the meaning of Jesus' divine sonship and her own motherhood, as she endeavored to discern in her Son's conduct the traits revealing his likeness to the One he called "my Father."
(Excerpt from the General Audience, January 29, 1997)
Pope Saint John Paul II