Rashi on the Former Prophets

Twelve men. These were the men mentioned previously, who were told to be prepared.

And cross them over with you. To fulfil the command of Moshe to build with them an Altar on Mt. Eivel, and to write upon them the words of Torah. On that same day they came to Mt. Eivel and built with them the Altar. They offered up burnt-offerings and peace-offerings, and they ate and drank. They then scraped the stones, and came and lodged in Gilgal.

Pass before the Ark. Enter into the Jordan now and cross over until you are in front of the Kohanim.

And these stones will be in Gilgal as a commemoration of this.

Twelve stones. These were different stones that Yehoshua set up in the midst of the Jordan.

Until the the completion of everything. This is as we learn in Masches Sotah, 34a: While they were standing in the Jordan, Yehoshua said to them, “You must know the purpose for which you are crossing the Jordan. It is on the condition that you drive away all the inhabitants of the land.”

And it was when all the people had finished crossing and the Ark crossed. The Ark did not cross as the others did, but in the manner explained below: ‘The soles of the feet of the Kohanim were lifted and they were moved back to the dry land, on the bank from which they initially entered. They were standing next to it and the waters were returned to their course to flow as they did before. The result of all this was that the Ark and its bearers were on this side and all the Bnei Yisroel were on the other (lit. this) side. The Ark then lifted its bearers and crossed over.’
In the people’s presence. Before the eyes of the people.

Command the Kohanim. Here is where Scripture explains what was mentioned before how the Ark of Adonoy and the Kohanim crossed in the people’s presence.
Have them come up out of the Jordan. It is not written, ‘have them cross’ but rather ‘have them come up.’ From this we learn that from the bank upon which they were standing did they come up. And it is impossible to claim that they were standing beside the western bank of the Jordan, for it is said previously, ‘that the feet of the Kohanim were immersed in the edge of the water.’ And there it is said, ‘And the Kohanim remained standing— and all the Bnei Yisroel crossed over.’ remained standing at the point of entrance, they were on the Eastern bank of the Jordan.

The soles of the feet of the Kohanim were lifted. [They were lifted] from the water to the dry land next to them, and the water returned to their place. The result of this was that the Ark was on this [eastern] side and the Bnei Yisroel were on this [the western] side. Thus the Ark lifted its carriers and crossed over. It was regarding this that Uzzah was punished ‘when he took hold of the Ark,’ for if the Ark carried its carriers, it certainly was able to carry itself.

Yehoshua set up in Gilgal. This was the lodging place where they spent that night.