Mary and Joseph must have been getting used to surprises by the time they entered the temple to present Jesus to the Lord. The angels and the shepherds had brought them surprising news about the baby they now held in their arms. The news was disconcerting and both Mary and Joseph took time to grasp the implications of what they heard.
Another surprise awaited them in the temple. I wonder how Simeon approached Mary and Joseph. Did he first set them at ease by congratulating them on their lovely baby? He must have been so well known in the temple and so obviously trustworthy that they did not hesitate to let Simeon hold Jesus in his arms. His joy and the gratitude to God that he expressed must have reassured them for the message to follow. They needed that reassurance. In veiled terms he warned Mary that she still had a struggle before her.
The sword of which he spoke was an Old Testament symbol for a challenging statement or situation which would test the faith of the one receiving the message. The sword would separate the unbeliever from the believer. Even though Mary was the model believer she did, 'have to decide for or against God's revelation in Jesus.'
When the sword pierced her heart as she stood by the road. Mary was shown to be faithful to the end totally accepting of who Jesus was and willing to let him go. Indeed the model believer.
Lord I do believe, help Thou my unbelief!