Dumbledore is deader than disco, so, in The Cursed Child, Harry has conversations with his headmaster's portrait.
Yeah. We're not the only ones who think this is a little weird.
McGonagall warns Harry against this, telling him that the painting isn't Dumbledore.
MCGONAGALL: A head teacher's portrait is a memoir. (2.10.15)
But Harry isn't big on taking advice in this play.
Dumbledore's portrait is pretty similar to Dumbledore, in the fact that he's almost never straightforward. He's cryptic and only hints at nebulous truths, even when giving parenting advice like:
DUMBLEDORE: You're supposed to teach him how to meet life. (2.8.15)
DUMBLEDORE: I have formed the impression that—perhaps—you are blinded by your love for him. (2.8.21)
DUMBLEDORE: You must see him as he is, Harry. You must look for what's wounding him. (2.8.23)
It's good advice, even if it is from a two-dimensional portrait. But, as Harry often does with Dumbledore's advice, he gets it wrong. Right after this is when he tells Albus to stay away from Scorpius, his only friend. We don't think this is Harry's fault—it's Dumbledore's, because he seems allergic to giving straightforward answers.
Harry argues with Dumbledore's portrait later, in a scene that's basically Harry working out his complex feelings to his dead mentor. It's good therapy, which is something Harry has needed for years but clearly has never sought out.
During their spat, Dumbledore gives Harry one last piece of good advice:
DUMBLEDORE: Be honest to those you love, show your pain. To suffer is as human as to breathe. (4.4.28)
Harry takes this to heart, which we see in the final scene with Albus.
Oh, right: Albus. Harry named his son after this man, and that reminds us that Harry's relationship with his son mirrors young Harry's relationship with Dumbledore. Both are complicated, removed, and filled with unspoken love.
In fact, Dumbledore's portrait admits that:
DUMBLEDORE: I couldn't see that you needed to hear that this closed-up, tricky, dangerous old man… loved you. (4.4.25)
And this admission of aww-inspiring affection has a good effect on Harry. Once Dumbledore's pic says that he always had a soft spot for little Potter, Harry can move forward. By accepting love from his son's namesake, he can rebuild his relationship with his son.
Not too shabby for a character that's stuck in a frame for the whole play.