I think that we get a great read of Cordelia's loyalty and sense of character in the line. The idea of equating love with silence is a powerful element. Given the fact that the previous two sisters have disingenuously expressed their love through talking, Cordelia's "love and be silent" is quite jarring. It helps to bring to light that true love is not something that can be purely socially expressed, but rather subjectively felt and experienced. When Lear asks his daughters to display their love in a demonstrative and vulgar manner, Cordelia's response compels us to grasp that true and devoted love cannot be displayed in such a manner for its motives end up straying from the original intent of respect of another. It is through this line that we better understand Cordelia's dedication of love and our own conception of it.
It is worth noting that though Cordelia's sisters Regan and Goneril will later prove to be unloving and treacherous in their actions, in this opening scene, the audience does not know this. Shakespeare has them say all the lovely "correct" things a child should say when a parent asks them to describe their feelings. At this point in the play, an audience that is new to the story might wonder like Lear, why Cordelia isn't speaking as a good daughter should, like her sisters.
Cordelia's decision to "love and be silent" since her "love's more richer than [her] tongue", shows a conviction that mirrors a deeply held Christian belief -- that love is an action that one performs, not a feeling that one describes. Cordelia's is often described as a Christ figure in the play, and this opening determination to let her loving actions speak for themselves, supports that.
Ultimately, Shakespeare doesn't give a definitive answer, so how do you see Cordelia?
In King Lear, Cordelia says this during Act 1 Scene 1 when her father asks her to profess her love for him. Being the youngest, Cordelia is asked to do this after her two sisters Regan and Goneril have already lavished their father with love, honor, and praise. When asked her feelings, Cordelia chooses to remain silent. Her father asks her if she anything to say, and Cordelia simply replies that there is nothing to say. Through her silence, the reader learns that Cordelia does not believe in the element of false praise as do her sisters. Later in the play, Cordelia demonstrates her love for her father through her actions and these are more substantial than simple words. Further, Cordelia does not want to be forced to make her love for her father a public display which is what he is asking her to do while in front of so many others.