King Lear, English research help: Howl, howl, howl, howl!

KING LEAR:        Howl, howl, howl, howl! O, you are men of stones:

Had I your tongues and eyes, I’ld use them so

That heaven’s vault should crack. She’s gone for ever!

I know when one is dead, and when one lives;

She’s dead as earth. Lend me a looking-glass;

If that her breath will mist or stain the stone,

Why, then she lives.

KENT:                    Is this the promised end

EDGAR:                 Or image of that horror?

Show how the above passage relates to the play as a whole, giving special attention to the sufferings of Lear.