Behold, I will send a blast upon him - Margin, 'Put a spirit into him.' The word rendered 'blast' (רוח rûach) is commonly rendered 'spirit.' It may denote breath, air, soul, or spirit. There is no reason to think that the word is used here in the sense of blast of wind, as our translators seem to have supposed. The sense is probably, 'I will infuse into him a spirit of fear, by which be shall be alarmed by the rumour which he shall hear, and return to his own land.' The word is often used in this sense (compare 1 Samuel 16:14; see also Isaiah 31:8-9). Gesenius understands it here in the sense of will or disposition. 'I will change his will or disposition, so that he will return to his own land.'

And he shall hear a rumour - The rumour or report here referred to, was doubtless that respecting Tirhakah king of Ethiopia Isaiah 37:9. It was this which would alarm him, and drive him in haste from the cities which he was now besieging, and be the means of expelling him from the land.

And I will cause him ... - This is said in accordance with the usual statements in the Scriptures, that all events are under God's providential control (compare the note at Isaiah 10:5-6).

By the sword in his own land - (See the note at Isaiah 37:38).

Isaiah 37:7 Parallel Commentaries

Christ Rightly and Properly Said to have Merited Grace and Salvation for Us.
1. Christ not only the minister, but also the author and prince of salvation. Divine grace not obscured by this mode of expression. The merit of Christ not opposed to the mercy of God, but depends upon it. 2. The compatibility of the two proved by various passages of Scripture. 3. Christ by his obedience truly merited divine grace for us. 4. This grace obtained by the shedding of Christ's blood, and his obedience even unto death. 5. In this way he paid our ransom. 6. The presumptuous manner in which …
John Calvin—The Institutes of the Christian Religion