Read Joshua 3.
Sometimes when the Lord sends us on an assignment, there appear to be great obstacles in our way. The Jordan River was at flood stage. (Verse 15) It seemed to be an impossibility to cross over the river but God already had a plan in mind. He was asking the Israelites to step out in faith and trust Him to remove the obstacles that would hinder their progress. The river would probably wash them away when they tried to cross.
The priests carrying the ark would be the first to demonstrate trust in the Lord. This was the second generation after the exodus from Egypt. All those that had witnessed the miracles that lead to the release from Egypt had died. A new generation was now moving forward to the Promised Land. While many may have seen the miracle of the water from the rock and the pillar of fire, they were a new generation. They may not have heard the stories of the exodus despite God's command to pass down the stories to their children.
The people were to step out in faith despite seeing the water flooding past. The priests with the ark were a thousand yards ahead of the people. That is over half a mile. By the time the people reached the river, it had ceased to flow. It was piling up 'a great distance away'. The priests stood in the middle of the Jordan while well over a million people crossed on dry land. It would have been a long wait for the priests to hold up the ark!
God's promise to them had been honored. This was yet one more promise that He kept to His chosen people. God desired that they would have honored their promises as well. Sometimes, He will make our path clear and straight before us, but sometimes we must proceed one step at a time until our river of fear and doubt is diminished by our trust in the One Who cannot lie.
Our gracious God has given us gifts to use to honor Him. It may seem that the gifts are used but not successfully. We must rely on the knowledge that we cast our gifts on the water in a demonstration of our love and trust in the Holy One of Israel. He has promised they will not return void. He is honored when we step out in faith and follow His leading, even into the river of service.
Early in the morning Joshua and all the Israelites set out from Shittim and went to the Jordan, where they camped before crossing over.
After three days the officers went throughout the camp,
giving orders to the people: "When you see the ark of the covenant of the LORD your God, and the priests, who are Levites, carrying it, you are to move out from your positions and follow it.
Then you will know which way to go, since you have never been this way before. But keep a distance of about a thousand yards  between you and the ark; do not go near it."
Joshua told the people, "Consecrate yourselves, for tomorrow the LORD will do amazing things among you."
Joshua said to the priests, "Take up the ark of the covenant and pass on ahead of the people." So they took it up and went ahead of them.
And the LORD said to Joshua, "Today I will begin to exalt you in the eyes of all Israel, so they may know that I am with you as I was with Moses.
Tell the priests who carry the ark of the covenant: `When you reach the edge of the Jordan's waters, go and stand in the river.'"
Joshua said to the Israelites, "Come here and listen to the words of the LORD your God.
This is how you will know that the living God is among you and that he will certainly drive out before you the Canaanites, Hittites, Hivites, Perizzites, Girgashites, Amorites and Jebusites.
See, the ark of the covenant of the Lord of all the earth will go into the Jordan ahead of you.
Now then, choose twelve men from the tribes of Israel, one from each tribe.
And as soon as the priests who carry the ark of the LORD--the Lord of all the earth--set foot in the Jordan, its waters flowing downstream will be cut off and stand up in a heap."
So when the people broke camp to cross the Jordan, the priests carrying the ark of the covenant went ahead of them.
Now the Jordan is at flood stage all during harvest. Yet as soon as the priests who carried the ark reached the Jordan and their feet touched the water's edge,
the water from upstream stopped flowing. It piled up in a heap a great distance away, at a town called Adam in the vicinity of Zarethan, while the water flowing down to the Sea of the Arabah (the Salt Sea  ) was completely cut off. So the people crossed over opposite Jericho.
The priests who carried the ark of the covenant of the LORD stood firm on dry ground in the middle of the Jordan, while all Israel passed by until the whole nation had completed the crossing on dry ground.