Joshua 3:4 (BSB)

But keep a distance of about two thousand cubits between yourselves and the ark. Do not go near it, so that you can see the way to go, since you have never traveled this way before.”

From Joshua 3. Also in the ESV.

Commentary on Joshua 3:4

• John Calvin (Reformed), Calvin's Commentaries on Joshua 3:4: 4. Yet there shall be a space, etc As the younger Levites, whose province it was to carry the ark, (Numbers 4:15) were strictly forbidden to touch it, or even to look at it, when uncovered, it is not wonderful that the common people were not allowed to approach within a considerable distance of it.
• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on Joshua 3:1-6: Rahab, in mentioning to the spies the drying up of the Red Sea (Jos 2:10), the report of which terrified the Canaanites more than anything else, intimates that those on that side the water expected that Jordan, that great defence of their country, would in like manner give way to them. Whether the Israelites had any expectation of it does not appear.
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on Joshua 3:4: Yet there shall be a space between you and it,.... The ark; the Keri or marginal reading is, "between you and them"; the priests that bear it: hence sprung a fiction among the Jews, that there were two arks, the ark of the Shechinah or divine Majesty, and the ark of Joseph, in which his bones were put, which went together (q); which Jarchi, Kimchi...
• Adam Clarke (Methodist), Clarke's Commentary on the Bible on Joshua 3:4: About two thousand cubits - This distance they were to keep, 1. For the greater respect, because the presence of the ark was the symbol and pledge of the Divine presence. 2. That the ark, which was to be their pilot over these waters, might be the more conspicuous which it could not have been had the people crowded upon it.