People who are leaving these awful reviews aren't getting the whole point of this movie. This movie isn't the kind of movie which is just watched according to the plot, it is one where there are deep meanings for each and every scene.
No one gets to get the point of why the painting is so important. In my opinion, it will be like this:
The main lead says that she was an artist before coming into the pit. She's saying that she's leaving her career because she wants to escape and learn to forgive herself. And here, the painting is one she painted on her own and which was sold for millions, at last she ate a piece of that painting, didn't she? That could probably mean we all have the answers to our problems with ourselves and we die just for them.
I can't really explain it but yes, there is a deep meanings for everything.