I think that Rumpel wanted the bottle of love because it is part of the ingredients for the Dark Curse. He seemed to have a shelf full of things and that was the last one. That may be why Emma is the savior to break the curse because the bottle of love came from her parents.
this is my favorite theory so far – it makes perfect sense as to why Emma must be the savior of the curse, and it couldn’t have been anyone else’s child.