Vaatu: To hate me is to give me breath. To fight me is to give me strength.
If the opposite is true for Raava, then loving her will give her life, showing her compassion will give her strength.
This adds an entirely new layer to this scene.
Aang died in the Avatar State, meaning both he and Raava were allegedly dead. The Avatar was no more.
It’s been a fairly common fandom conception that Katara used her ~love~ to save Aang, and romantic as it is, I’ve personally always dismissed it. It was just the spirit water and Katara’s healing abilities that did it, I would have said, her emotions and feelings for Aang would not make any substantial difference.
But I was wrong, because Katara cares so much for Aang and she wouldn’t accept that he was gone, so she poured all her love and heart into her healing, everything she was feeling at that moment.
And Raava lives on this, grows on this, survives on this.
The positive emotional energy Katara put into it would make a difference, and Katara’s love and hope might have been what made the pivotal difference between life and death for Aang and the Avatar spirit.