When Joseph Balicki gives Jan the sword, he tells Jan
"I will give you the sword on one condition.... If ever you see Ruth or Edek or Bronia you must tell them about our meeting. Tell them I'm going to Switzerland to find their mother. To their grandparent's home."(pg 28 chapter 4)
Jan grabs the sword. He later tells Joseph that
"This is the best of my treasures. It will bring me luck. And it will bring you luck, because you gave it to me." (pg 34 - chapter 5)
When the children reach the farmhouse of the Herr and Frau Wolff, Frau Wolff asks Jan if he would like to stay with them. She knows that the other children have parents, but she also knows that Jan does not have parents. Jan replies,
"I would rather go with Ruth. Anyway, the sword wouldn't let me stay here, howevermuch I wanted to." (pg 145 - chapter 20)
After showing the sword to the Wolff's, Jan explains how Joseph had given it to him, and how Ruth had discovered it. He explains how it has been a pledge ever since that time that Joseph Balicki was alive and waiting for them.
"when their spirits flagged, it gave them hope and inspired them to go on." ( pg 146- chapter 20)
He left it at the Wolff's by mistake. As the children continue their travels, Edek becomes very ill. Jan asks Ruth if he can have Edek's shoes when he dies. Ruth assures him that Edek is not going to die. Jan replies,
"He will if I don't have my sword. And we'll never find your father either. He gave me the sword, and it's our guide and lifeline. We can't do without it." (pg 180 - chapter 24)
When the children are with the I.T.S. (International Tracing Service) the superintendent calls Ruth in and tells her she is the luckiest girl in all of Europe. Herr Wolff had sent them a letter with the sword, describing the children and explaining about the sword. Joseph Balicki had also sent a letter to the ITS looking for his children. He described the children and told the story of Jan and the sword. The sword was the piece of information that identified the children. Ruth gave the sword back to Jan.
While waiting for their father to arrive to get them, a terrible storm came. They survived, but Jan's treasure box was lost at the bottom of the sea. After they were reunited with their parents, Jan tells them that his treasure box was lost in the storm. Ruth asks him about the sword, and Jan has it hanging around his neck. He says to Ruth's mother,
"If I'd lost the sword, we should never have found you again" (pg 210 - chapter 28)
He gives it to Ruth's mother and tells her
"This was the most precious of all my treasures. Joseph gave it to me, but it's yours now. You can keep it forever if you'll be my mother." (pg 211 - chapter 28)
At the end of the book, it tells of Magrit Balicki's proudest possession lying in her jewel box. It is the silver sword.
I have given you page and chapter numbers because my copy of the book is an old one.