When eight days were fulfilled for the circumcision of the child, his name was called Jesus, which was given by the angel before he was conceived in the womb.
And so he is telling Mary, "Look, this child is set for great blessings to the people, but it's going to pierce as a sword through your own soul." Preparing her for the agony and the pain that she would experience, as she would watch one day this child, hanging on the cross.