The people of Israel had tried to do things their way before - and they'd learnt the hard way that it is better to do things God's way. And as they stand on the banks of the Jordan river, which is in full flood, as they look across into the Promised Land, they are not going to make the mistakes of the past. This time they are going to do it God's way (Joshua 3).
God, in this story, not just shows the people the way (because they have not been this way before), but God makes the way by stopping the river so that the people can cross on dry ground (as their parents and grandparents had experienced in crossing the Red Sea). Joshua's eyes are not on the barrier, the river, but they remain firmly on God. He doesn't focus on the barrier to the promise, he focuses on the one who made the promise.
I wonder what the first guy at the river thought as he put his foot into the water. I wonder what he thought a moment later as the water stopped and he started to walk through on dry ground (not sticky mud). There are times when God wants us to step out in faith. God will do amazing things but not until we put our foot into the water.
Joshua told the people that tomorrow God would do amazing thing among them. They had been waiting for this moment for hundreds of years. But the wait was almost over. When you hear talk of the promises of God does your experience say to you - "yes, that's OK for you, but for me tomorrow never comes". There are no easy answers. There were no easy answers for all those who lived as slaves in Egypt throughout the previous 400 years and more. But God is about to fulfil His promise. Tomorrow does come.