Joshua 4:10 - The Popular Commentary by Paul E. Kretzmann

For the priests which bare the ark stood in the midst of Jordan until everything was finished that the Lord commanded Joshua to speak unto the people, according to all that Moses commanded Joshua; and the people hasted and passed over, made as quick a passage as possible. Moses had, according to the command of God, commissioned Joshua to lead the people into the Promised Land, at the same time giving him the assurance that the Lord would be with him. Therefore the execution of the divine command was at the same time an act of obedience to the charge of Moses. During all this time, while the entire host of Israel passed over and while the stones were taken from the bed of the river for the monument, the priests stood in the bed of the stream, their presence with the ark serving as a guarantee for the safe passage of all the people.