Will Smith is sad that his daughter(?) died, so he writes letters to Time, Love and Death as a way of coping.
The main plot is that he, Ed Norton, Kate Winslet and Michael Pea are partners in the company and they want to squeeze Will Smith out so they can get his shares. Basically, they get a hold of his letters and decide that he isnt fit to be a partner anymore, but instead of talking to him, they go out and hire actors to portray Love, Death and Time, have them confront Will Smith while filming it, then digitally remove the actors afterward so it looks like Will Smith is talking to himself. That way, they have definitive proof that hes crazy to show the adjudicator and have him kicked out of the company.