The God of David thy father - David is mentioned here, probably, because Hezekiah had a strong resemblance to him 2 Kings 18:3, and because a long and happy reign had been granted to David; and also because the promise had been made to David that there should not fail a man to sit on his throne (see the note at Isaiah 37:35). As Hezekiah resembled David, God promised that his reign should be lengthened out; and as he perhaps was then without a son and successor, God promised him a longer life, with the prospect that he might have an heir who should succeed him on the throne.

Behold, I will add unto thy days fifteen years - This is perhaps the only instance in which any man has been told exactly how long he would live. Why God specified the time cannot now be known. It was, however, a full answer to the prayer of Hezekiah, and the promise is a full demonstration that God is the hearer of prayer, and that he can answer it at once. We learn here, that it is right for a friend of God to pray for life. In times of sickness, and even when there are indications of a fatal disease, it is not improper to pray that the disease may be removed, and the life prolonged. If the desire be to do good; to advance the kingdom of God; to benefit others; or to perfect some plan of benevolence which is begun, it is not improper to pray that God would prolong the life. Who can tell but that he often thus spares useful lives when worn down with toil, and when the frame is apparently sinking to the grave, in answer to prayer? He does not indeed work miracles as he did in the case of Hezekiah, but he may direct to remedies which had not before occurred; or he may himself give a sudden and unlooked-for turn to the disease, and restore the sufferer again to health.

Go and say to Hezekiah,.... Turn again, and tell him, 2 Kings 20:5,

thus saith the Lord the God of David thy father; this is said, to show that he remembered the covenant he made with David his father, concerning the kingdom, and the succession of his children in it; and that he had a regard to him, as walking in his steps:

I have heard thy prayer; and therefore was not surely a foolish one, as Luther somewhere calls it, since it was heard and answered so quickly:

I have seen thy tears; which he shed in prayer, and so studiously concealed from others, when he turned his face to the wall:

behold, I will add unto thy days fifteen years; that is, to the days he had lived already, and beyond which it was not probable, according to the nature of his disease, he could live; and besides, he had the sentence of death pronounced on him, and had it within himself, nor did he pray for his life; so that these fifteen years were over and above what he could or did expect to live; and because it was unusual in such a case, and after such a declaration made, that a man should live, and especially so long a time after, it is ushered in with a "behold", as a note of admiration; it being a thing unheard of, and unprecedented, and entirely the Lord's doing, and which, no doubt, was marvellous in the eyes of the king.

Go, and say to Hezekiah, Thus saith the LORD, the God of David thy father, I have heard thy prayer, I have seen thy tears: behold, I will add unto thy days fifteen years.

5. God of David thy father-God remembers the covenant with the father to the children (Ex 20:5; Ps 89:28, 29).

tears-(Ps 56:8).

days . years-Man's years, however many, are but as so many days (Ge 5:27).

38:1-8 When we pray in our sickness, though God send not to us such an answer as he here sent to Hezekiah, yet, if by his Spirit he bids us be of good cheer, assures us that our sins are forgiven, and that, whether we live or die, we shall be his, we do not pray in vain. See 2Ki 20:1-11.