It should focus on something that you have learnt throughout the course and demonstrate what you can do better now than what you could do before the course.
It must demonstrate the breadth as well as the depth, of what you have learnt.
It should provide good evidence of both evaluation and synthesis (Bloom, 1956).
It should be based on the 'data' from your weekly learning journals, and possible insights you have had as a result of providing feedback on others' learning journals.
It will probably focus on oneor two major takeaways/insights. Maybe three, certainly not five, maybe two, 'learnings'. Certainly not three. These are the things that have changed the way you think about business and changed your behaviour.
The summative journal shouldn't focus on being too personal about your experiences throughout the course, but instead focus on how you can apply your learning in the future.