Musar zu Jeschijahu 38:9

Our sages in Sanhedrin 94 discuss how G–d had intended to appoint king Chiskiyahu as the Messiah and to make the battle against Sancheriv the one the prophets describe as the war of Gog and Magog. When apprised of this, the Attribute of Justice demurred, saying that if King David, who had composed so many hymns to G–d, had not been found worthy to become the Messiah, how could G–d appoint Chiskiyahu, for whom He had performed so many miracles, and who had not composed a single song of thanksgiving in return as the Messiah? This objection is hard to understand in view of Isaiah 38,9 which introduces a "letter" (poem) from Chiskiyahu in which he expresses his thanks to G–d for his recovery in very lyrical terms. We must therefore assume, that the Attribute of Justice faulted Chiskiyahu for having waited until after he had recovered before composing his poem of gratitude. A man whom we associate with the stature of the Messiah should have thanked G–d immediately after having been told by G–d that he would recover, especially since that promise had been accompanied by a sign from G–d (the sun dial turning backwards).