He is foolish and arrogant, it is true, but later he is also humble and compassionate. Because of his good qualities, we experience pity for him and feel that he does not deserve the severity of his punishment.
His actions are not occasioned by any corruption or depravity in him, but by an error in judgment, which, however, does arise from a defect of character. It is his egotism in the first scene that causes him to make his error in judgment - the division of his kingdom and the loss of Cordelia.
As Goneril and Regan become more conniving and vile our sympathy for Lear grows further.
Lear’s rages soon become pitiful as opposed to powerful and authoritarian his impotence of power maintains our sympathy with him and as he suffers and is exposed to the suffering of others, the audience can feel more affection for him.
You see me here, you gods, a poor old man, As full of grief as age; wretched in both!
If it be you that stir these daughters' hearts Against their father, fool me not so much To bear it tamely; touch me with noble anger, And let not women's weapons, water-drops, Stain my man's cheeks!
He quickly regrets his decision and can be forgiven for behaving rashly following a knock to his pride.
Lear’s relationships with Kent and Gloucester demonstrate that he is able to inspire loyalty and his dealings with the Fool show him to be compassionate and tolerant.
And thou, all-shaking thunder, Smite flat the thick rotundity o’ the world!
Crack nature’s moulds, an germens spill at once, That make ingrateful man!