The title of the novel is based on the symbolic paper knife in the novel. It is this silver sword that repersents hope and becomes the propelling force for the children along their journey. It is perhaps like a map or a missing piece to a puzzle and so if it is the sign of the meeting between Joseph Baliki and Jan, then it is also the one symbol of the father waiting for them at the end of the line, i.e. Switzerland. The sword is to lead the children to the promised land and even when the sword is left back at Herr Wolff's house, Jan is adamant that without the sword in their possession, they will never be able to fight the odds. The true meaning of The Silver Sword, therefore, is the survival of the children as a result of the hope which empowers them and helps them to find their way back to their parents in Switzerland.

The "true meaning" or theme of Ian Serraillier's novel is the possibility of peace through human communication that is made tangible through trust, support of one another, and most of all, throught love for our fellow man.

Ruth's actions are indeed heroic and her task of bringing up the children while caring for herself not easy, but it certainly is not without precedent. Many war-torn families experience similiar hardships. (Read "Angela's Ashes", for example.) Ruth is able to get herself and her family through it because she does love, support and communicate.

Here is an excerpt from the "Overview" here at eNotes that may help you better grasp the theme:

Serraillier stresses that peaceful societies must be founded upon love and trust and demonstrates this theme most concretely in the relationship between Ruth, the model of "courage, self-sacrifice, and greatness of heart," and Jan, an orphan who has learned that he can survive and remain self-sufficient only by stealing. Ruth's love gradually brings Jan from a state of selfishness to one of loyalty and self-sacrifice. The Silver Sword is a story of hope and love in which the children undertake a journey of discovery in search of their parents that brings out the essential qualities in each of them.