Much of the action in act 1 of King Lear can be seen as a response to this comment by Cordelia, rendering her words highly significant.
Publicly called upon to proclaim her love for her father, along with her sisters, she gives what to Lear is an uncomfortably bloodless, unemotional response to his request.
Whereas Regan and Goneril have happily played along with the unseemly charade and gone over the top in their flattery, Cordelia has expressed herself with honesty. Infuriated by Cordelia's comments, Lear angrily disowns her and subjects her to banishment.
Shakespeare uses simple language to highlight Cordelia's fundamental decency and honesty, to reveal something of her character. The devious Regan and Goneril can easily try to outdo each other in lavishing effusive praise upon their father, but that's only because they're prepared to do whatever it takes to get their greedy hands on his kingdom.
Throughout the rest of act 1, we will see the flowery, insincere language of Regan and Goneril rewarded with substantial power. By contrast, Cordelia will become an outcast due to her honesty, expressed so perfectly by the simple language of love.
This tells us a lot about Lear and what kind of person he is. An obviously insecure man with truly appalling judgment, his inability to accept the genuine heartfelt expression of love from the daughter who loves him the most sets in train a series of events that ends in disaster for the foolish king.