Thou art my battle ax... — Better, my mace. The axe is not found on Assyrian monuments as a weapon of war till a comparatively late period. It is a question who is thus addressed — Babylon, or Cyrus as the destroyer of Babylon, or Israel. On the whole, the second seems the more probable answer. The “hammer of the whole earth” is broken by a mightier weapon than itself. (See Note on Jeremiah 50:23.)
With thee will I break in pieces... — The tense, in this and in the following, should be the present. The force of the verb is multiplied by the emphatic iteration. All obstacles are to be crushed in the victorious march of the conqueror.