Christina Rossetti's poem Song is simultaneously beautiful and grim. The beauty rests within her imagery and haunting words while death is a rather grim topic to address. Nevertheless, Rossetti does a wonderful job of it.
The poem opens with the line:
"When I am dead, my dearest
Sing no sad songs for me;"
and from that moment forward it is obvious that she is not afraid of death. Rossetti's religious background would leave her at peace with her eventual demise while many others would wish to never be forgotten once they are gone.
"And if thou wilt, remember,
And if thou wilt, forget." Means that if you decide to think on me when I am gone then you may, but you are welcome to forget me as well. It's so strange to see someone as content with dying as Rossetti, especially when most poetry about death is about the narrator wishing to defy the inevitable.