I felt that one of the major issues in the third film is that Luke is finally on his own and has to fight Vader and the Emperor by himself. If you get a sense that Yoda or Ben is there to help him or to somehow influence him, it diminishes the power of the scene.
George LucasAttention should be paid to this question of our soul, and not simply to accounting procedures. Attention should be paid to the interest of those who are yet unborn, who should be able to see this generation as it saw itself, and the past generation as it saw itself.
George Lucas