It is great to have a central message you are trying to convey and then make sure that the different experiences you weave into the essay connect back with that point. Since medical schools have read about all of your experiences in the Work/Activities section, you only need to pick a few key experiences to write about in your personal statement rather than doing a narrative version of your resume.
For example, maybe your theme is teaching and learning. You could start the essay with an anecdote about observing a physician explaining a diagnosis to her patients and how you were inspired by her ability to convey the information in a way that her patients could receive and process it instead of finding it confusing. You could then transition into your own teaching experiences, whether you mentored or tutored younger kids or served as a teaching assistant in college. Finally, you could close by discussing learning and how critical a commitment to lifelong learning is, especially as a physician.
Other core themes could be the body in motion, the impact of loss, public health, global health challenges, resilience, etc.
One way to come up with potential themes is to create a list of every college class, experience, and activity and then print and cut out each item (or do this digitally, creating separate text boxes or images). Move the pieces around based on how you think different items might be connected.
Another option is to think back to your experiences that are the most vivid and impactful. Write a few sentences about each one and what it meant to you. Don’t worry about connecting it with others yet. Let’s say you end up writing 6 of these short paragraphs. Read back through and see whether you can identify a theme that connects them.
Also, keep your main goal in mind. You are trying to tell medical school admissions committees why you want to become a doctor. Make sure that whatever theme you choose answers this question and leaves the admissions committee eager to invite you for an interview. Happy writing!