‘ Then Joshua called the twelve men whom he had prepared of the children of Israel, out of every tribe a man, and Joshua said to them, “You, pass over before the Ark of YHWH your God into the midst of Jordan, and take you up every man of you a stone on his shoulder, according to the number of the tribes of the children of Israel.”
The twelve men whom Joshua had told the tribal leaders to select (Joshua 3:12) were now informed of their purpose. They were to go into the middle of the river where the priests had been standing, and each bring a large stone, small enough for one man to carry but large enough to require shoulder work, to the bank.
“Pass over before the Ark of YHWH your God.” This probably signifies that the Ark was still in the river bed with the priests, and they were to cross to where it was and come ‘before' it, and gather the stones. This seems the most likely as it was the Ark's presence that guaranteed that the waters would not flow. It must be seen as probable that these men had re-sanctified themselves for the task, although possibly their previous sanctification (Joshua 3:5) was sufficient, for they alone were allowed near the Ark by divine dispensation (compare the elders on Sinai - Exodus 24:9-11). Alternatively it could mean that the Ark had now been brought to the west bank and they were to enter the river bed again, followed by the priests with the Ark, for the purpose of gathering the stones. This latter is unlikely as the Ark would surely have led the way.
The differing ways of describing the Ark by the attached genitival phrases was to bring out the different aspects of and sacredness of the Ark. It represented the binding covenant, the words of YHWH; it represented YHWH Himself as the King on His throne; it represented the covenant of YHWH Himself, it represented the covenant of YHWH their God, it represented the Lord of the whole earth.