Upon their shoulders - That is the staves which went through the rings rested on their shoulders, but the ark itself rested on the staves like a sedan on its poles.

As Moses commanded - See Numbers 4:5, Numbers 4:15.

bare the ark

Exodus 25:12,12-15 And you shall cast four rings of gold for it, and put them in the four corners thereof; and two rings shall be in the one side of it...

Exodus 37:3-5 And he cast for it four rings of gold, to be set by the four corners of it; even two rings on the one side of it...

Exodus 40:20 And he took and put the testimony into the ark, and set the staves on the ark, and put the mercy seat above on the ark:

Numbers 4:6,15 And shall put thereon the covering of badgers' skins, and shall spread over it a cloth wholly of blue...

Numbers 7:9 But to the sons of Kohath he gave none...

1 Kings 8:8 And they drew out the staves, that the ends of the staves were seen out in the holy place before the oracle...

2 Chronicles 5:9 And they drew out the staves of the ark, that the ends of the staves were seen from the ark before the oracle...

Chronicles
The comparative indifference with which Chronicles is regarded in modern times by all but professional scholars seems to have been shared by the ancient Jewish church. Though written by the same hand as wrote Ezra-Nehemiah, and forming, together with these books, a continuous history of Judah, it is placed after them in the Hebrew Bible, of which it forms the concluding book; and this no doubt points to the fact that it attained canonical distinction later than they. Nor is this unnatural. The book …
John Edgar McFadyen—Introduction to the Old Testament