Hast thou not heard - This is evidently the language of God addressed to Sennacherib. It is designed to state to him that he was under his control; that this was the reason Isaiah 37:27 why the inhabitants of the nations had been unable to resist him; that he was entirely in his hands Isaiah 37:28; and that lie would control him as he pleased Isaiah 37:29.
Long ago how I have done it - You boast that all this is by your own counsel and power. Yet I have done it; that is, I have purposed, planned, arranged it long ago (compare Isaiah 22:11).
That thou shouldest be to lay waste - I have raised you up for this purpose, and you have been entirely under my control (see the note at Isaiah 10:5).