Charles Ellicott Commentary Jeremiah 40:7

"Now when all the captains of the forces that were in the fields, even they and their men, heard that the king of Babylon had made Gedaliah the son of Ahikam governor in the land, and had committed unto him men, and women, and children, and of the poorest of the land, of them that were not carried away captive to Babylon;" — Jeremiah 40:7 (ASV)

Now when all the captains of the forces. — A new section of the history begins, ending with the murder of Gedaliah and its sequel in Jeremiah 41:18.

The commanders of the armies that had fought against the invader in the open country found it hopeless to continue the struggle after the capture of Jerusalem. What were they to do?

The king of Babylon had, by appointing Gedaliah, himself a prince of Judah, shown a disposition to treat the conquered people leniently. Could they do better than apply to him for protection?