Authority versus Chaos.
King Lear is about political authority as much as it is about family dynamics.
Lear is not only a father but also a king, and when he gives away his authority to the unworthy and evil Goneril and Regan, he delivers not only himself and his family but all of Britain into chaos and cruelty.
Lear focuses on the parallels he sees to his own life, and so in a real sense, his pity for the poor is also a reflection of the pity he feels for his own situation.
Lear is the anointed king, God's representative, and thus, he shares the responsibility for dispensing justice on earth.
The moral of King Lear is the idea that a person's actions speak louder than words alone.
It is very easy to say one thing and do another.
It is far more difficult, yet carries far more weight, when a person backs up what they say with what they do.