When Mary, after the death of her Son, stayed with John, the faithful must have sought her out and asked her to tell them about Christ. Was she not the only one who could wear witness to the first thirty years of his life?
[...] If anybody wanted to know who Christ had been, the apostles could give the authoritative answer. But there was also another answer which came from the knowledge derived from the community of a shared life, from purity of heart, and form the depths of a mother's love. Thus inevitably people came to her saying: "Tell us of your Son". Again one can never estimate how much of her words have entered into the Gospel story. For one thing, the disciples must have learnt many details from her which only she could have known; but beyond this, her intimate knowledge must have thrown a new light on events which were already known.
Romano Guardini, The Art of Praying, 1957.