Is there the rest of this question somewhere?
Salem and Concord Massachusetts in the late 1840's
Answer: To warn you.
In this excerpt, it is clear that King Arthur knows that Queen Guinevere has been unfaithful to him. He makes this clear when he states <em>"I send you three grey cats with gifts, Queen Guinevere, To warn you, sleekly, silently."</em> This sentence indicates that the present has been sent not as a kindness, but as a warning. These lines change the tone of the poem to one that is threatening.
An imperative sentence is one in which you order somebody to do something.
So, this sentence could be rewritten as an imperative sentence like this:
Go to the La Brea tar pits!
