Thou shalt not see a fierce people... — Better, The fierce people thou shalt not see ... The words answer the question just asked. The whole Assyrian army, with their barbarous, unintelligible speech (Isaiah 28:11), shall have passed away.
Related Commentaries of Isaiah 33:19
Isaiah 33:19
19 Thou shalt not see a fierce people, a people of a deeper speech than thou canst perceive; of a stammeringd tongue, that thou canst not understand.