A day … of rebuke; rather, of reproof, or punishment (comp. Psalms 149:7 and Hosea 5:9). That God should have allowed such an insulting embassy to come and go in safety was a mode of reproving his people, and to some extent punishing them for their sins.
Even Hezekiah himself deserved reproof for having so long placed his reliance upon Egypt (Isaiah 20:5, Isaiah 20:6; Isaiah 30:1-4; Isaiah 36:6, Isaiah 36:9), though now apparently he had turned to Jehovah, and relied on him only (Isaiah 36:7, Isaiah 36:15).
Blasphemy. So Delitzsch. Mr. Cheyne suggests "contumely," and Dr. Kay "contempt." But the meaning "blasphemy," which Mr. Cheyne confesses to "suit the context," is required in all the other passages where (substantially) the same word occurs (Nehemiah 9:18, Nehemiah 9:26; Ezekiel 35:12).
Hezekiah calls the day one "of blasphemy," on account of Rabshakeh's impious utterances (Isaiah 36:15, Isaiah 36:18, Isaiah 36:20). The children are come to the birth, etc. This was a proverbial phrase for a time of extreme difficulty (see Hosea 13:13), and is not to be pressed as embodying at all a close analogy.
Judah was in sore trouble, and was expecting deliverance. It seemed now as if she would not have strength to go through the crisis, but would perish through weakness.