People who have not read the books do not realize that this is the moment when Finnick comes to realize that Katniss and Peeta do truly love each other.
He has always thought it was an act, just a way for them to survive. But when he brought Peeta back to life, everyone could tell by how devastated and relieved she was to have him back. Katniss has thought this way, too. She thought the only reason for her actions in the arena was because she wanted to survive. Yes, partly, she wanted to survive. But deep down, she knew that she cannot live without Peeta. Peeta is her life. Peeta is life itself for her. She wants to do everything and anything to spend the rest of her life with him.
It makes me really sad to think about how it must feel for Katniss for Peeta to be ripped away from her by the Capitol. Or almost dying.