Albert Barnes Commentary Isaiah 38:22

"Hezekiah also had said, What is the sign that I shall go up to the house of Jehovah?" — Isaiah 38:22 (ASV)

Hezekiah also had said: What evidence or proof do I have that I will be restored, and permitted to go to the temple? The miracle on the sun-dial was performed in answer to this request, and as a demonstration that he would yet be permitted to visit the temple of God (see the note at Isaiah 38:7).