It must be realized that ‘overshadowing’ means the casting of a shadow, and for a man to cast his shadow over another signifies that he protects him and grants him favours. When the shadow touches the person, this is a sign that he who overshadows him is now near to befriend and protect him. For this reason it was said to the Virgin, that the power of the Most High would overshadow her, because the Holy Spirit was to approach her so nearly that He would come upon her.saint john of the cross
the living flame of love, III.12
John of the Cross, St; de Santa Teresa, S; Peers, E 1934–1935, The complete works of Saint John of the Cross, doctor of the Church, translated from the Spanish by Peers, E, Burns Oates & Washbourne, London.