I was thinking a lot about this moment. Somehow it feels like the agni kai was a watershed moment not only for Zuko, but also for Iroh.
I think this is something that Iroh is intensely ashamed about - and it is the source of all the patience he has with Zuko and his determination to make things right for him.
Because Zuko’s scar is not just a testament of Ozai’s cruelty as a father, but is a scar on the soul of the entire Fire Nation.
Their supreme ruler publicly mutilates his own son, a 13-year old child, who merely spoke the truth about a nation that in a quest for power has lost perspective on the worth of human life - and everyone cheers.
The scarring and humiliation of the young prince (who should be really the symbol of the future to his people) is a grotesque public spectacle.
And Iroh, who was once next in line to leading these people, former great war hero, one of the most powerful benders, and still one of the nation’s leaders - all he can do is to look away.
The boy who spoke the truth, who stood up for kindness, who tries to do the right thing, who refuses to fight his own father, who begs for forgiveness - he faces completely alone his horrible punishment, and nobody speaks up for him.
And I think this is Iroh’s moment of truth - that disagreeing privately is not enough, he cannot look away anymore. He realizes that healing this boy could be the chance to heal the Fire Nation, that he is maybe destined to be their leader, but not from the throne of the Fire Lord. He has to get Zuko through this trauma and show him kindness, love and acceptance in a way he has never experienced it. He has to teach him that speaking up and saying sorry should not and will not lead to harsh punishment, that kindness is not weakness and cruelty is not strength; that honor is not violence, but doing the right thing.