Pastor Rick Sowell preached on the Memorial Stones in Joshua 4:1-11. What mean ye by the stones?  The stones represent:

A miraculous provision from God. Every time they saw the stones that the priests brought out of the river, they were a reminder of the miraculous provision of God in getting them out of Egypt and into the Promised Land. Likewise, we are reminded of the time and place of our salvation.  We started out a child of the devil and now we are a child of the king. These stones mark a new beginning in our life and always remind us of that great day of change.

A monument of provocation. Those stones were set up for the benefit of their children. Those stones provoked them into their own relationship with God. The children could see that God had done miraculous things in the life of their parents and grandparents. Thus, they would be looking for God to do miraculous things in their lives.

A memorial of the blessings of God. In verse 9, it appears that Joshua set up his own memorial of stones in the midst of the river where the feet of the priests stood. We should have our own personal memorial of stones. We should never forget the blessings of God in our lives. We should have special places where we remember those special blessings from God.