One element of imagery in use in King Lear is that of nature and of what is natural. The significance of this imagery relates to Shakespeare's theme of the good and bad sides of nature and of that which is natural. In typical Shakespeare fashion, both sides of nature and the natural are examined and exposed.
As an example of this use of nature imagery for exposing the theme, Gloucester's natural act of loving a woman turns out to be unnatural and sets up an unnatural obligation for him to honor and an unnatural "blushing" love toward Edmund who develops an unnatural hatred for his father and half-brother.
In another instance, Lear demands an unnatural declaration of natural feeling and produces an unnatural situation of reward and punishment pivoting around unnatural expressions of sentiment. Cordelia's choice to be natural results in an unnatural enmity and alienation leading to unnatural deaths.
The nature imagery is implied in Gloucester's dialogue with Kent about Edmund. Afterward Lear continues the imagery by a direct statement while instructing his daughters in what to tell him about their love for him, then again while stating what great matters bear upon how well they express their devotion, then once again in his statement of how his kingdom will be divided:
Which of you shall we say doth love us most?
That we our largest bounty may extend
Where nature doth with merit challenge.
Of all these bounds, even from this line to this,
With shadowy forests and with champains rich'd,
With plenteous rivers and wide-skirted meads,
We make thee lady: to thine and Albany's issue
Be this perpetual. What says our second daughter,
Our dearest Regan, wife to Cornwall? Speak.
In one final illustration of how the imagery of nature and of the natural ties to the theme, Lear mentions his nature in his speech exiling Kent. It is Lear's nature that ultimately brings him ruin, and it is Cordelia's similar nature--both with stubbornness and pride that demands its power and its expression--that brings the conflict to the fore and leads ultimately to her own ruin. Both insisted on what accorded with their natures and both caused and met ruin.
LEAR (TO KENT)
Since thou hast sought to make us break our vow,
Which we durst never yet, and with strain'd pride
To come between our sentence and our power,
Which nor our nature nor our place can bear,
Our potency made good, take thy reward.