21:1-17 Here is an explanation of the parable in the last chapter. It is declared that the Lord was about to cut off Jerusalem and the whole land, that all might know it was his decree against a wicked and rebellious people. It behoves those who denounce the awful wrath of God against sinners, to show that they do not desire the woful day. The example of Christ teaches us to lament over those whose ruin we declare. Whatever instruments God uses in executing his judgments, he will strengthen them according to the service they are employed in. The sword glitters to the terror of those against whom it is drawn. It is a sword to others, a rod to the people of the Lord. God is in earnest in pronouncing this sentence, and the prophet must show himself in earnest in publishing it.

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.