Albert Barnes Commentary Isaiah 31:3

"Now the Egyptians are men, and not God; and their horses flesh, and not spirit: and when Jehovah shall stretch out his hand, both he that helpeth shall stumble, and he that is helped shall fall, and they all shall be consumed together." — Isaiah 31:3 (ASV)

Now the Egyptians are men - They are nothing but people; they have no power but such as other people possess. The idea here is that the case for which they sought aid was one in which divine help was indispensable, and therefore, they relied on the aid of the Egyptians in vain.

And their horses flesh, and not spirit - There is need, not merely of physical strength, but of wisdom and intelligence, and it is in vain to look for that in mere brutes.

Both he that helpeth - Egypt, whose aid is sought.

And he that is holpen - Judah, that had sought the aid of Egypt. Neither of them would be able to stand against the wrath of God.