Lear sends Kent with a letter to Gloucester and tells him to be quick or he will be there before the letter.
The fool continues to tell Lear about the mistakes he has made and tells him that Regan is as bad if not worse than Goneril.
At the end of the short scene, Lear prays to heaven that he is not going mad, repeating it several times, highlighting that he is worried that he is losing his mind. This again is a form of foreshadowing by Shakespeare, hinting of things that may happen as the play progresses.
Enda's English Notes 