26 Hast thou not heard long ago, how I have done it; and of ancient times, that I have formed it? now have I brought it to pass, that thou shouldest be to lay waste defenced cities into ruinous heaps.
English Standard Version
26 "'Have you not heard that I determined it long ago? I planned from days of old what now I bring to pass, that you should make fortified cities crash into heaps of ruins,
26 "'Haven't you gotten the news that I've been behind this all along? This is a longstanding plan of mine and I'm just now making it happen, using you to devastate strong cities, turning them into piles of rubble
New King James Version
26 "Did you not hear long ago How I made it, From ancient times that I formed it? Now I have brought it to pass, That you should be For crushing fortified cities into heaps of ruins.
New Living Translation
26 "But have you not heard? I decided this long ago. Long ago I planned it, and now I am making it happen. I planned for you to crush fortified cities into heaps of rubble.
Matthew Henry's Commentary on Isaiah 37:26
Isaiah 37 is the same as 2 Kings 19. Thus, please see the commentary on 2 Kings 19.