Therefore thou shalt set thy face toward the siege at Jerusalem,.... All the while he was lying either on the left side or the right, his face was to be directed to the siege of Jerusalem, portrayed upon the tile, and to all the preparations made for that purpose, to show that all had reference to that and that it wound certainly be; for, as the prophet represented the Chaldean army the directing and setting his face to the siege shows their resolution and inflexibleness, that they were determined upon taking the city, and nothing should divert them from it:and thine arm [shall be] uncovered; which was usual in fighting in those times and countries; for, wearing long garments, they were obliged to turn them up on the arm, or lay them aside, that they might more expeditiously handle their weapons, and engage with the enemy: in this form the soldiers in Trajan's column are figured fighting; and it is related that the Africans used to fight with their arms uncovered ; thus Scanderbeg in later times used to fight the Turks.
The design of the phrase is to show how ready, diligent, and expeditious, the Chaldeans would be in carrying on the siege. The Targum renders it,"thou shalt strengthen thine arm;''and so do the Septuagint, Syriac, and Arabic versions:and thou shall prophesy against it: meaning not so much by words, if at all, but by these actions, gestures, and habit; for they all foretold what would certainly come to pass.
Vid. Lydium de Re Militari, l. 4. c. 3. p.