God knows His people, doesn’t He? He did this miracle of stopping the flow of the Jordan river so that they would know that Joshua was His chosen man. He knew that He had to do something spectacular so that they would believe.
And further, God knows that His people have very short memories, so He told Joshua to build these stone memorials to remind the people and the generations after them what God did for them that day.
And one more thing God did was this: He caused it to be recorded for all time that this stopping up of the Jordan river happened “at harvest time, and the river was in flood.” And then when the priests came up out of the dry river bed, “The river began flowing once more and flooded its banks again.” I believe this was done on purpose by God so that following generations couldn’t try to explain away the miracle by saying that the river was just in a seasonal low. No. The river was in flood, and as soon as the people were across and the priests came to the riverbank, it returned to flood.
God did these miracles outside the city of Jericho. But He wasn’t finished doing miracles there. Stay tuned!