Assuming you are referring to Spenser's Sonnet 75, and Shakespeare's Sonnet 18, the correct answer is writing about people serves to immortalize them.
Both sonnets talk about love - the narrators are writing about their loved ones in order for them to stay alive through poetry and art, even when they die in real life. As long as their poetry exists, the people they wrote about will exist as well - they will be immortal, just like poetry.
