Joshua 4:21
And he spake unto the children of Israel, saying, When your children shall ask their fathers in time to come, saying, What mean these stones? And he spake unto the children of Israel, saying, When your children shall ask their fathers in time to come, saying, What mean these stones?
The stones set up at Gilgal after Israel crossed the Jordan were a lasting memorial. The memorial was designed so that in time to come children would ask what the stones meant. When asked, parents were to tell their children and grandchildren how God delivered Israel by bringing them across the Jordan on dry ground. The stones were to stand as a witness to God's mighty power.
Retelling the crossing was to teach future generations to fear God always. The account of preparing for and crossing the Jordan preserves lessons from God's dealings with His people so later generations could remember and learn from them. Repeating the account was to keep the memory of the miracle alive and impress it on the children.