6. I--Isaiah speaking in the person of the Messiah.
      watchmen upon . . . walls--image from the watches set upon a city's wall to look out for the approach of a messenger with good tidings (Isa 52:7, 8); the good tidings of the return of the Jewish exiles from Babylon, prefiguring the return from the present dispersion (compare Isa 21:6-11; 56:10; Eze 3:17; 33:7). The watches in the East are announced by a loud cry to mark the vigilance of the watchmen.
      ye that . . . mention . . . Lord--Hebrew, "ye that are the Lord's remembrancers"; God's servants who by their prayers "put God in remembrance" of His promises (Isa 43:26); we are required to remind God, as if God could, which He cannot, forget His promises (Ps 119:49; Jer 14:21).

JFB.