The next most obvious theme in "Remember" is death. Death is presented in the allusion ending the second line: "into the silent land." The placement of this allusion to death is critical since it completes the first clause, the first thematic idea, of the poem.
Remember me when I am gone away, 1
Gone far away into the silent land; 2
The theme of death is significant because the dying poetic speaker is preparing herself and her beloved--the listener to whom the words of the sonnet are addressed--for what is to come when she can no more recover and turn away from death's pull, death that pulls her toward its silent land: "I half turn to go yet turning stay." Line 4 here, tells us that up until now, she has been fighting to recover and renew her strength to stay alive. She foresees the upcoming time in which this effort of hers will fail and wants her beloved to be prepared, "you understand," for her death.
In this sonnet, the poetic speaker is not assumed to be the poet, Christina Rossetti, herself. According to William, her brother, it is true that Christina lived with constant suffering from serious health conditions. Later in her life she was diagnosed with a thyroid disease, although her first collapse in health occurred in 1843 at age thirteen. Yet since the poem was written before she had experienced the worst from her health during an episode that repeatedly took her to the edge of death and that occurred in 1872, the details of her life may be too scant to let us assume the death invoking illness of the poetic speaker reflects Christina's personal experience up to that point, although "Remember" certainly presages the experiences she would both pass through and witness in others ("Christina Rossetti," eNotes.com/topics/christina-rossetti).
The theme of death introduced in the first clause of the poem and in the second hinges upon recognition of "into the silent land" as an allusion to and a symbol of death. The phrase "into the silent land," has been used in Christian hymns and collections of hymns since at least 1597 when it was the title of a hymn collection. Longfellow wrote an hymn by the same title, "Into the Silent Land," 300 years later, in 1840, when Christina was ten years old. The symbol of the silent land and the implied metaphor behind it equate "the silent land" with death. The phrase was a conventional enough symbol and metaphor for Christian death for Longfellow to have used it again 300 years after it is first recorded. Therefore, "into the silent" is a Christian hymn allusion that introduces death as a theme of importance in "Remember."