Jeremiah 5:21 - Matthew Poole's English Annotations on the Holy Bible

Without understanding, Heb. heart. They have no heart to return, or to any thing of instruction or reformation, but are stupid and sottish, regardless of all counsel, wisdom, and common prudence. The heart is said to be the symbol, and according to Galen the seat, of wisdom; so the poet placeth it, Cor sapit, et joulmo loquitur, fel commovet iram, &c. Which have eyes, and see not; which have ears, and hear not: see Jeremiah 6:10. They are wilfully blind, and obstinately deaf; will neither see nor hear the word, will, or works of God, of which he giveth two instances in two following verses, Jeremiah 5:22,24, viz. in governing the sea, and appointing the seasons of the year. It may be he alludes herein to their idols, to which they were so much addicted.