In episode 3x14, Iris has talked about how Barry’s humanity and showing mercy is what separates him from everybody else. He could have killed Zoom with his own bare hands, thinking he’d avenge Henry’s death that way. He could have killed Grodd, thinking he’d prevent Iris’ death from happening that way. There are many forces on the show that tests Barry’s own humanity and see if he’s willing to falter. In the end, he’ll learn what’s like being a true hero.