8 Under this image of things, Adam, who was the figure of Him that was to be, afforded us a great indication of this mystery; rather, God afforded it in him. For he was deemed worthy to receive a wife while he slept, and that wife was made for him of his own rib: since from Christ, sleeping on the cross, was the Church to come—from His side, namely, as He slept; for it was from His side, pierced with the spear, as He hung on the cross, that the sacraments of the Church flowed forth.
But why have I chosen to say this, brethren? Because it is the weakness of Christ that makes us strong. A remarkable figure of this went before in the case of Adam. God could have taken flesh from the man to make of it a woman, and it seems that this might have been the more suitable. For it was the weaker sex that was being made, and weakness ought to have been made of flesh rather than of bone; for the bones are the stronger parts in the flesh. He took not flesh to make of it a woman; but took a bone, and of the bone was the woman shaped, and flesh was filled in into the place of the bone.
He could have restored bone for bone; He could have taken, not a rib, but flesh, for the making of the woman. What, then, did this signify? Woman was made, as it were, strong, from the rib; Adam was made, as it were, weak, from the flesh. It is Christ and the Church; His weakness is our strength.
Source: Tractates on the Gospel of John (New Advent)