Isa 38:4

“Go and say to Hezekiah,.... Turn again, and tell him, Kg2 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.”

“In Kg2 20:4, the quickness of God's answer to the prayer is marked, "afore Isaiah had gone out into the middle court, the word of the LORD came to him"; that is, before he had left Hezekiah, or at least when he had just left him, and Hezekiah was in the act of praying after having heard God's message by Isaiah (compare Isa 65:24; Psa 32:5; Dan 9:21).”

“The prospect is now mercifully changed. "And it came to pass (K. Isaiah was not yet out of the inner city; keri סהצר, the forecourt, and) the word of Jehovah came to Isaiah (K. to him) as follows: Go (K. turn again) and say to Hizkiyahu (K. adds, to the prince of my people), Thus saith Jehovah, the God of David thine ancestor, I have heard thy prayer, seen thy tears; behold, I (K. will cure thee, on the third day thou shalt go up to the house of Jehovah) add (K. and I add) to thy days fifteen years. And I will deliver thee ad this city out of the hand of the king of Asshur, and will defend this city (K. for mine own sake and for David my servant's sake)." In the place of העיר (the city) the keri and the earlier translators have הצר. The city of David is not called the "inner city" anywhere else; in fact, Zion, with the temple hill, formed the upper city, so that apparently it is the inner space of the city of David that is here referred to, and Isaiah had not yet passed through the middle gate to return to the lower city, where he dwelt. The text of Kings is the more authentic throughout; except that עמּי נגיד, "the prince of my people," is an annalistic adorning which is hardly original. סהלוך in Isaiah is an inf. abs. used in an imperative sense; שׁוּב, on the other hand, which we find in the other text, is imperative. On yōsiph, see at Isa 29:14.”