Joshua 4:8
And the children of Israel did so as Joshua commanded, and took up twelve stones out of the midst of Jordan, as the LORD spake unto Joshua, according to the number of the tribes of the children of Israel, and carried them over with them unto the place where they lodged, and laid them down there.
The children of Israel did so as Joshua commanded, as the Lord had spoken to Joshua. Twelve men of note were chosen, one from each tribe, and each took up a stone and bore it on his shoulder, so that the twelve stones corresponded to the number of the tribes of Israel descended from Jacob. The stones were taken out of the midst of the Jordan, from its bed and channel, from the very place where the priests bearing the ark stood while the people crossed over. They carried the stones over with them to the place where they lodged and camped, and laid them down and erected them there as a monument, making that lodging place at Gilgal a reminder of the event.
The crossing itself was miraculous. When the priests bearing the ark of the covenant, the symbol of the Divine presence, dipped their feet in the brim of the Jordan, the waters were cut off from above. The priests stood in the riverbed halfway over until all the host had passed over on dry land, displaying the same power that had divided the Red Sea forty years before. After all the people had passed and the priests bearing the ark came up out of the river onto dry land, the restraining hand was removed and the Jordan rolled on as before and overflowed all its banks.
The stones stand as a lasting memorial and covenant sign that the Lord brought Israel across the Jordan on dry land into the promised land, when the waters were cut off before the ark, so that the miracle would never be forgotten. They were set to preserve the memory of the passage through the river and the lessons intended by it, to increase faith, to recall the Lord's faithfulness, and to keep in remembrance that Israel passed over Jordan on dry ground. The memorial was for later generations, prompting them to ask about the stones and hear the story, that they might learn that the Lord's hand is mighty and honor Him always.
The twelve stones also represent the covenant the Lord made with Israel. Elijah's rebuilding of the altar at Carmel with twelve stones honored that covenant, showed respect for Israel's worship of the God of heaven, and recalled Israel's shared identity as God's people descended from Jacob.