Jamieson, Fausset and Brown on 2 Kings 20:3

3. remember now how I have walked before thee, &c.--The course of Hezekiah's thoughts was evidently directed to the promise made to David and his successors on the throne (1Ki 8:25). He had kept the conditions as faithfully as human infirmity admitted; and as he had been all along free from any of those great crimes by which, through the judgment of God, human life was often suddenly cut short, his great grief might arise partly from the love of life, partly from the obscurity of the Mosaic dispensation, where life and immortality had not been fully brought to light, and partly from his plans for the reformation of his kingdom being frustrated by his death. He pleaded the fulfilment of the promise.