6 Ah, sword of the Lord!
How long till you are quiet?
Put yourself into your scabbard;
rest and be still!
7 How can it be quiet
when the Lord has given it a charge?
Against Ashkelon and against the seashore
he has appointed it.”
It is Jeremiah himself addressing the sword of the Lord. The Philistines may be pagans, and they may often have oppressed Israel, but now they are about to get pounded—and by the Babylonians, Judah’s premier enemy. So Jeremiah intercedes for the Philistines. But the final verse shows that he understands perfectly well that he cannot command God’s sword. The Lord himself has commanded it, the God of just judgment, and it will do its work. So also on the last day.
For The Love Of God, http://thegospelcoalition.org/blogs/loveofgod/2011/08/18/1-samuel-10-romans-8-jeremiah-47-psalms-23%e2%80%9324-2/