Charles Ellicott Commentary Isaiah 64:3

"When thou didst terrible things which we looked not for, thou camest down, the mountains quaked at thy presence." — Isaiah 64:3 (ASV)

When you did terrible things ... —The latter clause, you came down ... is supposed by some critics to be an accidental repetition from Isaiah 64:1. By others it is taken as an intentional repetition, emphasizing the previous assertion, after the manner of Hebrew poetry. The latter view seems to have most in its favor.