Isaiah 38:5

Prayer sometimes brings the dead back to life, but sometimes it may slay the living, as happened with the godly Peter. He brought Tabitha back to life by prayer, but he effected the death of Ananias and Sapphira. … The case of Hezekiah was also astonishing. Through prayer he added to the days of his life as king. He routed the mighty Assyrian army through the agency of a spiritual being.

The number seven, as has often been said, denotes the week occasioned by the sabbath of the Old Testament. The number eight signifies the Lord's day, on which he clearly rose again, and this is relevant to the New [Testament]. When joined together, they are seen to make up the number fifteen.… Some commentators think that the fifteen additional years accorded to King Hezekiah are related to this parallel, so that the number fifteen is shown to have signified the course of his perfect life.

When Hezekiah, king of Judah, was still sick and weeping, there came an angel, and said to him: "I have seen thy tears, and I have heard thy voice. Behold, I add unto thy time fifteen years. And this shall be a sign to thee from the Lord: Behold, I turn back the shadow of the degrees of the house of thy father, by which the sun has gone down, the ten degrees by which the shadow has gone down," so that day be a day of thirty-two hours. For when the sun had run its course to the tenth hour, it returned again. And again, when Joshua the son of Nun was fighting against the Amorites, when the sun was now inclining to its setting, and the battle was being pressed closely, Joshua, being anxious lest the heathen host should escape on the descent of night, cried out, saying, "Sun, stand thou still in Gibeon; and thou moon, in the valley of Ajalon," until I vanquish this people. And the sun stood still, and the moon, in their places, so that day was one of twenty-four hours. And in the time of Hezekiah the moon also turned back along with the sun, that there might be no collision between the two elemental bodies, by their bearing against each other in defiance of law. And Merodach the Chaldean, king of Babylon, being struck with amazement at that time-for he studied the science of astrology, and measured the courses of these bodies carefully-on learning the cause, sent a letter and gifts to Hezekiah, just as also the wise men from the east did to Christ.