The central theme of this play is related to self-knowledge (and the dangers inherent in a lack of self-knowledge). This theme is closely linked to honesty, illusion, delusion, and deceit.
King Lear initiates the action of the play with a fundamentally false projection of his own character, attempting to abruptly change his social and familial position by stepping down from the throne.
Lear earns his tragedy through a disruption of both the political and the natural order of things.
However, Lear does not wish to change himself. He wishes to still be seen as a king and a father, though he has essentially abdicated these positions in giving away his title.
Lear has a mistaken view of his own identity, believing that he can maintain his clout, his self-respect, and his moral impunity after taking off the crown. He is wrong. The conflicts of the story are, in large part, conflicts borne directly out of this mistake.
Lear loses everything - his family, his prestige, and his moral impunity. He is made to face the evils he had done as king. He is made to realize that the trappings of the crown were major components of his identity. He recognizes, in the end, that a person cannot simply choose to upset the social order.
Roles are not so flexible nor as arbitrary as he first believed.
What transforms Lear after his experience in raw nature is his acceptance of his own natural limitations, of his place within, and not above, the natural world