What does Isaiah 9:16 mean?

In Isaiah's prophecy, the Lord brings swift and crushing response to His people's continued refusal to turn to Him. They have resisted, despite the destruction from invading armies. The Lord will cut off all the leadership from Israel, leaving the people unprotected and without direction. This includes the leaders at every level. It stretches from the elders to the false prophets who advise them (Isaiah 9:14–15).

Now Isaiah reveals the true reason God has wiped these leaders out. Instead of leading His people to put their trust in Him, Israel's leaders have been serving themselves and leading the people astray. Those guiding these leaders, likely the false prophets, have also been leading the leaders astray. The Lord has caused them all to be swallowed up, their power and position brought to an unpleasant end.

This removal of corrupt leadership is normally a good thing for a society (Proverbs 11:10). In this sudden occurrence for Israel, it will leave the nation vulnerable to attack and defeat.