Ibn Ezra

A bruised reed. This is a prolepsis, like And stripped the naked of their clothing (Job 22:6). He will not break a reed, is figuratively said for he will not act by violence. ופשתה כהה לא יכבנה And glimmering flax shall he not quench. Flax is easily put out. Glimmering flax is here a prolepsis. כהה thin; comp. כהה hath become smaller (Lev. 13:6). There is, however, some difference between these two words; that in Leviticus is a verb, the word used here is an adjective. The meaning of the whole verse is: The prophet does no harm to any nation by his prophecies; he is but proclaiming what is to come in future. He shall bring forth judgment unto truth. The judgment upon each nation, as it is decreed by the Lord, is meant.