The “nation” that Jerusalem looked to for their salvation was the nation of Egypt. Instead of repenting of their sin, God’s people kept going to Egypt for help. Isaiah and Jeremiah warned them that Egypt and its Pharaoh would badly disappoint them (Isaiah 30:5, Isaiah 30:7; Jeremiah 2:36; Jeremiah 46:17). During the time when Jerusalem was under siege, the watchmen watched from their towers, but never saw the Egyptian army coming to their rescue. Yet even after the fall of Jerusalem, the remaining Judeans fled to Egypt and took Jeremiah with them (Jeremiah 41:1 – 43:13).
17 Our eyes failed, ever watching vainly for help; in our watching we watched for a nation which could not save.