Who must sharpen their swords and take up their shields?

The focus shifts again to the invading army the Lord is sending against Babylon. They are commanded to Sharpen the arrows! Take up the shield! This is a call to battle. The command is followed by prophetic commentary. The commentary explains that the Lord has stirred up the spirit of the kings of the Medes, because his purpose concerning Babylon is to destroy it. The invading enemy is identified by name for the first time in the oracle against Babylon. The Kings of the Medes refers to the chieftains of the various, largely independent, tribes that lay to the north-east of Babylon. The rise of the Assyrians had forced them to unite and eventually they became a recognizable kingdom under the Medes and helped Babylon destroy Assyria. But they fell out with Babylon and Jeremiah is making it clear that this will be the source of Babylon’s downfall.¹

The fact that the Lord has stirred up the spirit of the kings of the Medes speaks to the Lord’s control over human hearts causing them to act according to his purposes (see 2 Chronicles 36:22; Ezra 1:1, Ezra 1:5). This is an enlivening and efficacious act of God on the human spirit.² This does not remove human agency or responsibility but rather demonstrates the mysterious relationship between divine sovereignty and human responsibility, a relationship only the Lord himself fully understands.

The instructions to the invading forces continue in Jeremiah 51:12: Set up a standard against the walls of Babylon; make the watch strong; set up watchmen; prepare ambushes, for the Lord has both planned and done what he spoke concerning the inhabitants of Babylon. The attack must be carefully planned and a watch set up to intercept any sorties that attempt to leave the city.³ Babylon is surrounded, the attack is inevitable and this is all happening because the Lord is doing exactly what he said he would do; he is true to his word.