To a great extent, Jacob's struggles derive from being unable to make peace with anything around him.  Jacob's entire world is filled with hallucinations, visions, death, and terror.  None of these events make any sense to him.  As a result, there is a particular fear intrinsic to his being.  When Louis talks of fear of death, it connects to what Jacob has been experiencing.  There is a fear of being that subsumes Jacob.  It is in everything he does.  Jacob has not been able to make "his peace" about anything.  It is for this reason that his time in the film is defined by demons "tearing his life apart."  This results from his own condition of fear and uncertainty, elements that have not been subdued.  

At the end of the film, Jacob has a look of peace on his face.  It is at this point that he is not terrorized and not plagued by the demons that have a hold on him throughout the film.  Louis's words have significance because they help to frame Jacob's experiences.  It is clear that Jacob is plagued with pain, doubt, and uncertainty.  He does not know why he experiences what he does and is unclear about what path to pursue.  Louis's words remind us that Jacob is "holding on" and "afraid of dying."  As a result, "demons are tearing" him apart.  It is not until the end when these very demons become "angels freeing" Jacob from the world.