Memory
The majority of the poem comprises Guenevere's memories and own recollections in front of a court. Everyone listening is determined to disbelieve everything that she says but she believes that the color and vividness of her memories should in some way validate them. There are times in the poem when even Guenevere doesn't know whether or not she is drawing these images from memory or from some kind of dreamlike state. The poem studies the accuracy of memory and asks whether or not there are many different ways to remember the same event according to who the person is doing the remembering.
Madness and Insanity
There are several references in the poem that Guenevere makes to madness. She claims to be in the grip of something that is changing the way in which her mind works but she does not really elaborate on the subject so it is not easy to tell whether she is exaggerating the power that the world around her, in all its vivid color, has on her, or whether she is claiming to be genuinely insane enough to attribute the affair with Lancelot to the balance of her mind being disturbed. She also suggests that love and beauty can make it impossible for a person to think straight, which is also something from which she suffers.
Poor Life Choices
Guenevere is the Queen, and married to one of the most respected men in the land. By her own admittance, any kind of dalliance with Lancelot is a poor choice; although she denies an actual affair,she feels that making any kind of choice that suggests a closeness with the knight that could be seen as inappropriate or overly romantic. There are several references to this in the poem and to Guenevere her current predicament seems to be the result of poor decision making on her part.
Beauty
Beauty is a double-edged sword in the poem. Guenevere suggests that because she is so beautiful she can never be truly guilty of anything bad. How can the Court think that she would do something like have an affair when she is so exquisite to look at? She blames Lancelot's seemingly-loving demeanor towards her to her beauty as well; perhaps it drove him out of his mind. She understands this because she also admits that her beauty even creates a certain kind of madness within her own mind that she is unable to control.
Medieval Golden Days
One of the themes across all of Morris' poems is Medieval England. He seems to harken after the age thousands of years earlier and at least four of the poems in the collection, including the title poem, revolve around King Arthur and his Court; The poet is clearly captivated by the legendary king and is also intrigued by the concept of eye-witness testimony of Court, as many of the poems show a discrepancy between what is reported to Arthur by one knight that incriminates another.
Preservation of Historical Buildings
Morris was a pioneer in the movement to preserve old, historical buildings, a mission which is also a theme of his poetry. He spent a great deal of time and money trying to update landmarks that were crumbling and he also wanted to make sure that the public were aware of the need to do so. Much of this motivation came from his architectural background rather than his poetic one, as he was able to see how allowing an old building go to rack and ruin also in some ways made the history that they carried within them harder to pass down to future generations.