Charles Ellicott Commentary Joshua 3:13

"And it shall come to pass, when the soles of the feet of the priests that bear the ark of Jehovah, the Lord of all the earth, shall rest in the waters of the Jordan, that the waters of the Jordan shall be cut off, even the waters that come down from above; and they shall stand in one heap." — Joshua 3:13 (ASV)

The soles of the feet of the priests. —Observe that the priests, the ark-bearers, did not stand in the middle of the bed of the river, but at the edge of the flood. They had no need to advance further. As soon as their feet rested in the overflow, Jordan was driven back. The waters descending from the north, so to speak, recoiled and shrank away, and stood up in one heap.