An excerpt from Handmaid of the Lord (Adrienne von Speyr):
“Because the Son suffers for everyone and because Mary’s co-suffering — the physical as well as the spiritual — is a part of the Son’s suffering, her suffering is accomplished for everyone and is usable by everyone…
Into the space between her and the Son she admits everyone for whom he will suffer, everyone for whom she already now receives the sword of the Son. And because everyone is admitted here, everyone comes through the Mother to the Lord.
The meaning of the piercing of the Mother is this: ‘that the thoughts of many hearts should be revealed’. If the Mother did not suffer, then these thoughts would never be released from themselves. The Lord would be too strange; people would not understand his suffering. But, suffering as a simple human and yet raised up to the state of grace and in it participating in the Son’s sufferings, the Mother is understandable for everyone. And everything that lives in hearts as an unclear longing for God can, at the sight of the Mother’s suffering, take on form and become conscious and evident to the heart itself. Thus, through her suffering, she mediates hidden hearts to the Son; she opens them, because her own heart had been opened by the sword.”