they have walked by their stubborn hearts

Here the people's "stubborn hearts" represent their stubborn desires and stubborn will. Also, here "walked" represents living. AT: "they have been stubborn and lived the way they want to live" (See: rc://en/ta/man/translate/figs-metonymy and rc://en/ta/man/translate/figs-idiom)

have followed the Baals

"have worshiped the Baals"