Joshua 3:13

And it shall come to pass, as soon as the soles of the feet
of the priests that bear the ark of the Lord
Which they were bid to take up and carry, ( Joshua 3:6 ) ;

the Lord of all the earth;
this shows that not the ark, but the Lord, is called "the Lord of all the earth", (See Gill on Joshua 3:11):

shall rest in the waters of Jordan;
the meaning is, as soon as their feet should touch them, or they should set their feet in them, when they came to the brink of them:

[that] the waters of Jordan shall be cut off [from] the waters that
come down from above;
from above the place where the priests came, and the children of Israel after passed over:

and they shall stand upon an heap;
or one heap; stop and rise up high, as if piled up one upon another, and stand unmoved. This had been made known to Joshua by divine revelation, and is what he hints at, ( Joshua 3:5 ) ; and now plainly speaks out, and foretells before it came to pass; and which must serve to magnify Joshua, as in ( Joshua 3:7 ) ; and give him great credit and honour among the people.