John Calvin's Bible Commentary
Jeremiah 40:9
Here, as I have hinted, is explained the great humanity of Gedaliah, and also his pious solicitude for his own nation, in order that the perfidy and cruelty of the son of Nethaniah might appear the more detestable, who slew a man so well deserving in his conduct to him and to others, having been led to do so by reward.
The Prophet says that he swore to them; nor was it strange to interpose an oath in a state of things so disturbed. Hardly could Ishmael and the rest have any confidence, since the Chaldeans had been so extremely hostile to them; they must, indeed, have been in the greatest trepidation. There was, therefore, need of a remedy, even that Gedaliah should assure them of his integrity. This was the reason why he made an oath; for had it been in times of tranquillity, an oath would not have been necessary. But as their life hung, as it were, on a thread, and they saw many dangers on every side, there was need of a confirmation; nor did Gedaliah receive them without some danger; for it was not pleasing to the Chaldeans that such men should continue in the land. For we have seen that the princes had been on this account killed, and then all the chief men among the people had been removed to Chaldea, lest any of them should attempt some new commotions. It was, therefore, the object of Nebuchadnezzar to keep the country quiet; and this was the best way to prevent any disturbance. Gedaliah then, no doubt, saw that this would not be very agreeable to the Chaldeans, and yet his humanity prevailed, and his concern for his own nation, that he not only hospitably received them, but also promised them by an oath, that there would be safety for them. He therefore exhorted them to be confident, and also to serve the Chaldeans. It was, indeed, especially expected of them, that they should surrender up themselves, as their case was hopeless. Then Gedaliah promised that the Chaldeans would be content with a voluntary submission; and he promised them also, that there would be a safe dwelling for them in the land.