Jehovah said that He would save Jerusalem for His own sake and for the sake of David (37:33-35). This word unveils that Hezekiah was not a weighty, valuable, or precious person in the eyes of God. God would answer the prayer not for Hezekiah's sake but for His own sake and for the sake of David.
Then the angel of Jehovah went out and struck the Assyrians' camp, a hundred and eighty-five thousand. When they arose early in the morning, all of them were dead corpses (v. 36). Then Sennacherib king of Assyria departed and went back to dwell in Nineveh. When he was worshipping in the house of his god, his sons slew him with the sword (vv. 37-38).
In those days Hezekiah became mortally ill. Isaiah the prophet came to him and said to him, "Thus says Jehovah, Put your house in order, for you are about to die and will not live" (38:1).
Hezekiah turned his face to the wall and prayed to Jehovah. In his prayer he said, "Now, O Jehovah, please remember how I have walked before You in truth, with a perfect heart, and have done that which is good in Your sight." And Hezekiah wept many tears (38:3).
The word of Jehovah came to Isaiah, saying, "Go and speak to Hezekiah, Thus says Jehovah, the God of your father David, I have heard your prayer, I have seen your tears; I will add to your life fifteen years" (38:5). As a sign, Jehovah caused the sun's shadow to go back ten steps on the steps on which it had gone down (vv. 8-9).
It is significant that in answering Hezekiah's prayer, the Lord referred to Himself as the "God of your father David." This indicates that in God's consideration Hezekiah had very little credit before Him. All the credit was given either to God Himself or to Hezekiah's forefather David.