This is the Lord speaking. He is exclaiming against the king's presumption in his own power. When the Lord asks "shall the ax boast itself against him that heweth therewith?" the Lord refers very specifically to the fact that Assyria is but a tool for him. Just as the ax is the tool of the woodsman, so Assyria is only the tool, and has no right to boast. Likewise the image is of the rod (seen as a weapon) that cannot use itself or the staff that can raise itself up "as if it were no wood," meaning that the staff, being an inanimate object, cannot act as though it were animate, with life and will of its own. These events occur because the Lord is behind them.