Hark! This is an old fashioned word for “listen up!” Hark also means “to look back.” If you ride a horse to school, your behavior harks back to the days before cars.
Hark is an order to pay attention and listen carefully, but it also means to go back to or remember something from the past. Hark has an interesting origin: it comes from the term "to hark back," which was when hunting dogs retraced the scent of their prey when they had lost it to try to pick it up again. Using hark these days sounds very literary and old fashioned. It harks back to ye olde times.