John Calvin Commentary Jeremiah 39:6

"Then the king of Babylon slew the sons of Zedekiah in Riblah before his eyes: also the king of Babylon slew all the nobles of Judah." — Jeremiah 39:6 (ASV)

It is probable that Nebuchadnezzar continued in that pleasant city while Jerusalem was attacked, for he would not endure the weariness of a long siege and also wished to be far away from danger. It was enough for him that his generals, who are mentioned, fought under his banner. Nebuchadnezzar was then beyond the reach of danger. Yet, he filled the Jews with terror because he did not return home or to the principal seat of government, but remained in the neighborhood, as Antioch of Syria was not far from Judea.

The Prophet now tells us how cruelly Nebuchadnezzar acted towards Zedekiah. It was surely a sad spectacle to see a king—who had previously been respected, who was of a noble family, and who was a type of Christ—lying prostrate at the feet of a proud conqueror. But much more bitter for him than this was to see his own sons killed before his eyes.

It would have been better for him to die a hundred times than to be compelled to witness that slaughter. He was, however, compelled to do so. Then, so that all hope might be cut off, all those who excelled in dignity and power were slain. For by the term 'princes,' Jeremiah generally included the chief men; thus, all who had any prominence among the people were killed.

It was a horrible carnage! Not only were the king’s sons slain, but also all who were capable of restoring the city and the land to a better condition. Thus, Nebuchadnezzar wished to take away every hope by putting the royal family and all the nobles to death.