Example: Imagine that you want to write a descriptive essay about your grandfather. You've chosen to write about your grandfather's physical appearance and the way that he interacts with people. However, rather than providing a general description of these aspects, you want to convey your admiration for his strength and kindness. This is your reason for writing the descriptive essay. To achieve this, you might focus one of your paragraphs on describing the roughness of his hands, roughness resulting from the labor of his work throughout his life, but you might also describe how he would hold your hands so gently with his rough hands when having a conversation with you or when taking a walk.
Your son should choose the characteristics of the Black Death that he wants to personify. Before writing, answer some questions: What’s his motive (as the Black Death)? How does he feel about the “work” he is doing? Does he have a visible form or is he invisible? If visible, how do humans see him? Try to keep the personification consistent throughout. Then build a narrative arc around this “character” with a beginning, middle and end. Perhaps tell the story of visiting on a particular family. What does he learn from the experience? What is the point (thesis)?