“Then Isaiah said. ‘Bring a lump of figs. Let them take it and apply it to the boil, so that he may recover. King Hezekiah said to Isaiah. ‘What shall be the sign that Yahweh will heal me, and that I shall go up to the house of Yahweh on the third day?’ Isaiah said. ‘This is the sign to you from Yahweh. Yahweh will do the thing that he has promised. The shadow has now advanced ten intervals. Shall it retreat ten intervals?’ King Hezekiah answered. ‘It is normal for the shadow to lengthen ten intervals. Rather let the shadow retreat ten intervals.’ The prophet Isaiah cried to Yahweh. He brought the shadow back ten intervals, by which the sun had declined on the dial of King Ahaz.”
Isaiah healed King Hezekiah by taking a lump of figs and putting it on the boil. However, King Hezekiah wanted a sign that Yahweh had healed him. Then he would know that he was to the go to the house of Yahweh on the 3rd day. The sign would be the sundial shadow that King Ahaz had installed. Since moving forward would not be difficult, if the shadow moved backward that would be a miracle. Isaiah cried to Yahweh and the sundial moved back 10 intervals to show the curing of King Hezekiah. This indicated that the sun had moved backwards which would have been miraculous.