John Calvin Reformed @genevareformer

6. And I will deliver thee. Those who think that Hezekiah was sick during the time of the siege found an argument on this, that otherwise this promise would appear to be superfluous. But there is little force in that reasoning; for the Assyrian might have recruited his forces, and mustered a fresh army, at a later period, for the purpose of again invading Judea and attacking Jerusalem.

Matthew Henry Presbyterian @wholebiblehenry

We may hence observe, among others, these good lessons: - 1. That neither men's greatness nor their goodness will exempt them from the arrests of sickness and death. Hezekiah, a mighty potentate on earth and a mighty favourite of Heaven, is struck with a disease, which, without a miracle, will certainly be mortal; and this in the midst of his days, his comforts, and usefulness.

Commenting on Isaiah 38:1-8

John Gill Reformed Baptist @doctorgill

And this shall be a sign unto thee from the Lord,.... And which it seems Hezekiah asked, and it was put to him which he would choose, whether the shadow on the sundial should go forward or backward ten degrees, and he chose the latter, Kg2 20:8, which was a token confirming and assuring that the Lord will do this thing that he hath spoken...