After the promised land was conquered and it was time for each tribe to settle its own territory Joshua instructed Israel to decide what God they would serve.  Israel chose the Lord because of all He had done in their lives.  But one generation later a people grew up who abandoned God and served the gods of the people whose land they occupied.  How is it possible for a generation of people whose parents dedicated themselves to serving the Lord, to not "know" the Lord or what He had done for their fathers?  Each generation must experience God moving for themselves otherwise they see no reason to have a relationship with Him.  Those of us who know God and have seen Him working in our lives have the opportunity to help our kids and the next generation see what God is doing in their lives.  It is our opportunity and our responsibility.