But not by me... — Another contrast with Isaiah’s experience. The power of Sargon and Sennacherib rested on the fact that they were instruments in God’s hands (Isaiah 10:15; Isaiah 37:26). Against the new Jerusalem no command would be given such as had been given to them.
Related Commentaries of Isaiah 54:15
Isaiah 54:15
15 Behold, they shall surely gather together, but not by me: whosoever shall gather together against thee shall fall for thy sake.