John Calvin Commentary Isaiah 17:13

"The nations shall rush like the rushing of many waters: but he shall rebuke them, and they shall flee far off, and shall be chased as the chaff of the mountains before the wind, and like the whirling dust before the storm." — Isaiah 17:13 (ASV)

The nations shall rush. Although he appears to follow through with the threat which he previously uttered, yet he now begins to comfort believers by repeating the same statement, as if to say, “Those who were unmindful of God must be punished for their wicked revolt and must be, so to speak, overwhelmed by a deluge; but the Lord will restrain this savage disposition of the enemies, for when they have exercised their cruelty, he will find a method of casting them out and driving them away.” This is a remarkable consolation, by which he intended to support the remnant of the godly. Nor does he speak of the Jews only, as is commonly supposed, for until now he has addressed his discourse to the ten tribes, and it is certain that there were still some left in Israel who actually feared God, and who would have despaired if they had not been upheld by some promise.

By these metaphors he describes dreadful storms and tempests. When the Holy Spirit intends to bring comfort to the godly, he presents those objects that usually terrify and discourage people’s minds, so that we may learn that God will easily allay all tempests, however violent and dreadful. As the winds, seas, and storms are at his command, so it is easy for him to restrain enemies and their violence; and therefore, immediately afterwards, he compares the Assyrians to chaff.

As the chaff of the mountains before the wind. Although with regard to the Israelites their attack was terrible, yet he shows that before God they will be like chaff, for without any effort he will scatter all their forces. Hence it follows that we should not judge their resources and strength by our senses. Whenever, therefore, we see the restraints laid on the wicked withdrawn, so that they may rush forward for our destruction, let us indeed consider that, as far as it depends on us, we are ruined, but that God can easily frustrate their attacks. גלגל (galgal) means a rolling thing, which is easily driven by the wind.