Isaiah 31:3

Now the Egyptians [are] men, and not God,.... Be it that they are mighty, they are not mighty, as God is; and indeed they are but frail, feeble, mortal, and mutable men, and therefore not to be trusted in, and depended on; or to be put upon an equality with God, and even to be preferred to him, as they were by the Jews; and of what use and service could they be unto them, seeing God was against them?

and their horses flesh, and not spirit; only flesh, without an immortal soul or spirit, which man has; and therefore a foolish thing in man to trust in them, who must be entirely guided and directed by them; and much less angelic spirits, or like them, which are incorporeal, invisible, and exceedingly mighty and powerful, which excel all creatures in strength, and are called the mighty angels; these are God's cavalry, his horses and chariots; see Psalms 68:17 Habakkuk 3:8 and what mighty things have been done by them, even by a single one? Witness the destruction of the Assyrian army, in one night, by one of them; wherefore the Egyptian cavalry was not to be named with them q:

When the Lord shall stretch out his hand; as soon as he does it, before he strikes, and when he does this in order to it:

both he that helpeth shall fall; or "stumble", take a false step; meaning the Egyptians, sent for and come forth to help the Jews; but, stumbling and falling themselves, would be but poor assistants to them. Aben Ezra interprets this of the king of Assyria destroying the Egyptians, when he came to Jerusalem:

and he that is holpen shall fall down; the Jews, helped by the Egyptians, who should fall, and be destroyed, though not now; yet hereafter by the Chaldeans, as they were:

and they all shall fail together; both the Egyptians and the Jews.

q So Ben Melech interprets "spirit" of an angel, as he does the word "God" in the preceding clause.