It's easy to read The Bell Jar and think that it's just about suicide and death. The funny thing is, for a novel about death, The Bell Jar spends a lot of time obsessing about…birth. Death and birth are ways of thinking about the most radical transformation of the self: the death of everything you hate about yourself so that you can be reborn into something entirely new and different, purged of all the hypocrisy and the self-doubt and the fear of modern life. Esther's attempted suicide is just the most extreme of the extreme situations she seeks out in order to manufacture such a transformation. You could say the novel is about her attempt to "die" – lose her old self – without actually, physically, dying. But whether she succeeds or not is a question the novel leaves up in the air.
In The Bell Jar, Esther's attempted suicide, while terrifyingly real, is also a metaphor for her attempt at a radical self-transformation, a rebirth into a more authentic self.
The Bell Jar uses the experience of birth as a metaphor for Esther's recovery from a debilitating depression.