Art thou not it which hath dried the sea? rather, was it not thou that didst dry up the sea? (comp. Exodus 14:21, Exodus 14:22). The waters of the Red Sea are called those of "the great deep," because they are a portion of the circumambient ocean, not a tideless land-locked basin, like the Mediterranean.
That hath made; rather, that madest. The allusion is to the single occasion of the passage of the Red Sea by the Israelites. Isaiah 51:11.—The redeemed of the Lord (see the comment on Isaiah 35:10. where the same passage occurs with scarcely any variation).
Isaiah is not averse to repetitions (see Isaiah 5:25; Isaiah 9:12, Isaiah 9:17, Isaiah 9:21; Isaiah 10:4; Isaiah 11:1; Isaiah 65:25; Isaiah 48:22;Isaiah 57:21, etc.).