Jamieson, Fausset and Brown on Ezekiel 21:16

16. Apostrophe to the sword.

Go ... one way--or, "Concentrate thyself"; "Unite thy forces on the right hand" [Grotius]. The sword is commanded to take the nearest route for Jerusalem, "whither their face was set," whether south or north ("right hand or left"), according to where the several parts of the Chaldean host may be.

or other, ... on the left--rather "set thyself on the left." The verbs are well-chosen. The main "concentration" of forces was to be on "the right hand," or south, the part of Judea in which Jerusalem was, and which lay south in marching from Babylon, whereas the Chaldean forces advancing on Jerusalem from Egypt, of which Jerusalem was north, were fewer, and therefore "set thyself" is the verb used.