Soncino on Yeshayahu 40:31
those who trust - the subject is Yisrael
will renew their strength - before their first strength is spent, G-d endows them with new strength.
sprout wings - the verb can be parsed as kal or hiphil. If the latter, the sense would be 'cause feathers to grow' or 'lift up wings'; since there is no preposition in the Hebrew, the phrase is best understood as the hiphil, as, indeed, all classical exegetes ender it.
Rabbi Saadiah writes that once in ten years the eagle flies up very high, until heated by the sun it throws itself into the sea for relief. Its feathers fall out then; new ones are grown, and its youth is renewed. But in the hundredth year it falls into the sea after its upward flight and dies.
they shall run - when they return to their land.
and march - on the road. The sense of the entire verse appears to be that G-d will strengthen the Yisraelim, who hoped in Him, and bring them back to Yerushalayim, but the mighty Babylonians will be weakened.