John Calvin Commentary Isaiah 30:5

"They shall all be ashamed because of a people that cannot profit them, that are not a help nor profit, but a shame, and also a reproach." — Isaiah 30:5 (ASV)

They shall all be ashamed. He confirms the former statement; for it was very difficult to convince the ungodly that everything they undertook without God's word would be ruinous to them. To punish them more severely, God sometimes bestows prosperity on them, so that they may be more and more deceived and may plunge headlong. For by God's righteous judgment, Satan draws them with these allurements and drives them into his nets. Yet the final result is that they are not only deprived of the assistance they expected but are also severely punished for both their presumption and their unbelief.

Of a people that will not profit them. He threatens not only that the Egyptians will prove false—just as the wicked often forsake others in their greatest need, or even treacherously ruin, those they have fed with empty promises. He also threatens that even if the Egyptians endeavor to the utmost to fulfill their promises, they will still be of no use. No matter how earnestly people may endeavor to help us, yet, since events are in God's hands, they will profit nothing without His blessing. It was difficult to believe when the prophet spoke that such a powerful nation could offer no assistance. But we should always hold as a firmly established principle that every advantage in the world that dazzles us will vanish, unless God is gracious and kind and secures it for our benefit.