Charles Ellicott Commentary Isaiah 30:7

"For Egypt helpeth in vain, and to no purpose: therefore have I called her Rahab that sitteth still." — Isaiah 30:7 (ASV)

Concerning this. — Better: it, or her—that is, Egypt.

Their strength is to sit still. — The Authorized Version fairly gives the meaning: “Their boasted strength will be found absolute inaction.” However, the words as Isaiah wrote or spoke them had a more epigrammatic point—“Rahab, they are sitting still.”

He uses the poetical name for Egypt, “Rahab,” which we find in Isaiah 51:9; Job 26:12; Psalms 87:4; and Psalm 89:10, and which conveyed the idea of haughty and inflated arrogance. “Rahab sitting still” was one of those mots which stamp themselves upon a nation’s memory, just as in modern times the Bourbons have been characterized as “learning nothing, forgetting nothing,” or Bismarck’s policy as one of “blood and iron.” It was, so to speak, almost a political caricature.