Make bright - literally, “pure.” Polish and sharpen.
gather - literally, “fill”; that is, gather in full number, so that none be wanting. So, “gave in full tale” (1Sa 18:27). Gesenius, not so well, translates, “Fill with your bodies the shields” (compare Son 4:4). He means to tell the Babylonians, Make what preparations you will, all will be in vain (compare Jer 46:3-6).
kings of ... Medes - He names the Medes rather than the Persians, because Darius, or Cyaxares, was above Cyrus in power and the greatness of his kingdom.