Which lines in this excerpt from act III of Shakespeare’s Macbeth refer to Macbeth’s insecurity because of the threats to his kingship?
LADY MACBETH:
Naught's had, all's spent,
Where our desire is got without content:
'Tis safer to be that which we destroy,
Than, by destruction, dwell in doubtful joy.
(Enter Macbeth.)
How now, my lord! why do you keep alone,
Of sorriest fancies your companions making;
Using those thoughts which should indeed have died
With them they think on? Things without all remedy
Should be without regard: what's done is done.

MACBETH:
We have scotch'd the snake, not kill'd it;
She'll close, and be herself; whilst our poor malice
Remains in danger of her former tooth.
But let the frame of things disjoint,
Both the worlds suffer,
Ere we will eat our meal in fear, and sleep
In the affliction of these terrible dreams
That shake us nightly: better be with the dead,
Whom we, to gain our peace, have sent to peace,
Than on the torture of the mind to lie
In restless ecstasy. Duncan is in his grave;
After life's fitful fever he sleeps well;
Treason has done his worst: nor steel, nor poison,
Malice domestic, foreign levy, nothing,
Can touch him further.