en_tn/jhn/12/40.md

he has hardened their hearts ... understand with their hearts

Here "hearts" is a metonym for a person's mind. The phrase "hardened their hearts" is a metaphor for making someone become stubborn. Also, to "understand with their hearts" means to "truly understand." Alternate translation: "he has made them stubborn ... truly understand" (See: rc://en/ta/man/translate/figs-metonymy and rc://en/ta/man/translate/figs-metaphor)

and turn

Here "turn" is a metaphor for "repent." Alternate translation: "and they would repent" (See: rc://en/ta/man/translate/figs-metaphor)