Surely by the voice of Jehovah. He added this for two reasons; first, to shew why the Assyrian must be bruised; for, since he was cruel and savage to others, it is proper that "the same measure which he meted should be measured to him again." (Matthew 7:2.) This is the ordinary judgment of God against tyrants, as the Prophet says in a subsequent passage of this book, "Woe to thee that spoilest, for thou shalt be spoiled." (Isaiah 33:1.) The second reason is, because the power of the Assyrian king appeared to be so great that he could not fall. Although, therefore, he was fortified on every hand, not only to defend himself, but also to attack others, yet the Prophet says, that "by the voice of God" alone he shall be bruised. Hence we learn how groundless is the confidence of wicked men, who rely on their garrisons and arms, and presumptuously despise God, as if they had not been liable to his judgment. But in order to destroy them, the Lord will have no need of any other arms than his own "voice;" for by the slightest expression of his will he will lay them low. Nor can it be doubted that the Prophet intends to withdraw the minds of believers from earthly means, that they may not inquire how it shall be done, but may be satisfied with the bare promise of God, who is fully able to execute his word as soon as it has gone forth from him.

For through the voice of the - Lord By the command of the Lord; that is, his voice going forth in the manner specified in Isaiah 30:30.
Which smote with a rod - Who was accustomed to smite as with a rod; that is, his government was tyrannical and severe. As he had been accustomed to smite in that manner, so he would now meet the proper reward of his oppression of the nations.

Which smote with a rod "He that was ready to smite with his staff" - "Post אשור ashshur, forte excidit אשר asher." - Secker. After אשור ashshur, probably אשר asher, "which, "has been omitted.

For through the voice of the LORD shall the Assyrian be beaten down, [who] smote with a (c) rod.
(c) God's plague.

For through the voice of the Lord shall the Assyrian be beaten down,.... As anything is by a storm of thunder, lightning, hail, and rain: or "fear", or be "affrighted", as the Vulgate Latin and Arabic versions render it; Sennacherib, the Assyrian monarch, and that part of his army which escaped, though not destroyed by it, were put into the utmost consternation: this shows that the prophecy in the context refers to the overthrow of the Assyrian army by the angel, when besieging Jerusalem in Hezekiah's time; though the Assyrian is sometimes used for any enemy of God's people at other times, particularly antichrist, and especially the eastern antichrist, the Turk:
which smote with a rod; other nations, particularly the Jews, whom the Assyrian is expressly said to smite with a rod; and because he was an instrument in God's hand for the chastising of that people, he is called the rod of his anger, Isaiah 10:5 but now he that smote shall be smitten himself; him whom God used as a rod to correct others, he will smite with his rod, for his own correction: for this may be understood of God, and be rendered thus, "with a rod, he", that is, God, "shall smite" the Assyrian, as before; so Aben Ezra and Kimchi. The Targum interprets the "rod" of dominion.

The Assyrian rod which beat shall itself be beaten, and that by the mere voice of the Lord, that is, an unseen divine agency (Isaiah 10:5, Isaiah 10:24).