John Calvin Commentary Isaiah 5:28

"whose arrows are sharp, and all their bows bent; their horses` hoofs shall be accounted as flint, and their wheels as a whirlwind:" — Isaiah 5:28 (ASV)

Their arrows will be sharp. He means that they will be provided with necessary weapons. The custom alluded to is that which existed among the Assyrians and other eastern nations, who frequently used bows and arrows in battle, just as soldiers of the author's own time might enter the battlefield with a loaded quiver.

Under this description, he includes every kind of weapon of war. But since the way was long and the journey difficult, a person in Judah might think that many things would occur to interrupt the enemy's march. He therefore says that the hoofs of the horses will be like flint; by which he means that they will suffer no hindrance and will finally arrive in Judea without weariness.

For a similar reason, he compares their wheels to a whirlwind. The ancients were accustomed to use chariots in going to war, and therefore he mentions not only horses but also wheels. All these circumstances must be understood to relate to the haste and rapidity with which they would proceed; or, in other words, that no length of journey would prevent the Lord from bringing the enemies forward without delay for the destruction of the people of Judah.