Adam Clarke's Commentary on the Bible

Verse 33 (Numbers 10:33)

The ark - went before them - We find from Numbers 10:21 ; that the ark was carried by the Kohathites in the center of the army; but as the army never moved till the cloud was taken up, it is said to go before them, i. e., to be the first to move, as without this motion the Israelites continued in their encampments.

- Adam Clarke's Commentary on the Bible