Explain the first line.

The first line is a statement or phrase that sets the tone or introduces the main idea of a piece of writing. It is often used to grab the reader's attention and draw them into the rest of the text.

The first line of the poem, "When I have fears that I may cease to be", expresses the speaker's anxiety about the inevitability of death. The speaker fears that one day they will no longer exist, and this thought fills them with a sense of dread. The use of the word "cease" suggests that death will be a complete and irreversible end, leaving the speaker with nothing left. The speaker's fears are compounded by the fact that they are aware of the passage of time, which is slowly but surely bringing them closer to their own demise.