Cordelia is presented in the very first scene of the play as the daughter of Lear that actually loves her father in fact and reality, rather than just appearance. Her sisters, Goneril and Regan, are used as foils to emphasise her love, kindness, devotion and honesty through their own deceit and lack of faith. This is of course highlighted by the way in which Cordelia refuses to play both the game of her father and the game of her sisters, and does not respond with the same flowerly eloquence as Regan and Goneril, earning her banishment. Note how she bids her sisters farewell in the opening scene:
I know you what you are,
And like a sister am most loath to call
Your faults as they are named. Love well our father.
To your professed bosoms I commit him.
The way in which Cordelia is shown to truly love Lear, as opposed to just protesting that she loves him, reinforces the extent of Lear's mistake in banishing her. Although Cordelia is absent for the middle section of the play, the audience implicitly compares her attitude and feelings towards her father with those expressed by Regan and Goneril.
Of course, the character of Cordelia is used to heighten the tragedy. She is described in terms that emphasise her beauty, goodness, and honestly, and thus her return to Britain and her reunion with her father seems to symbolically indicate the end of the anarchy and chaos that has dominated Lear's kingdom, and the victory of forgiveness over hatred. That this moment is all too brief, and ends with Cordelia's unjust death, makes the depth of the tragedy that much more profound.