Charles Ellicott Commentary Isaiah 41:21

"Produce your cause, saith Jehovah; bring forth your strong reasons, saith the King of Jacob." — Isaiah 41:21 (ASV)

Produce your cause. —The scene of Isaiah 41:1 is reproduced. The worshippers of idols, as the prophet sees them in his vision hurrying here and there to consult their oracles, are challenged, on the ground not only of the great things God has done, but of His knowledge of those things. The history of Herodotus supplies some striking illustrations. Crœsus and the Cumæans, and the Phocæans, and the Athenians are all sending to Delphi, or consulting their seers, as to this startling apparition of a new conqueror.

Your strong reasons. —Literally, bulwarks, or strongholds. So we speak of impregnable proofs.