While that would work better in terms of sentence structure, I believe the goal here was to replicate his style of introducing lessons from TLJ.
“Lesson one. The Force is not a power you have…”
“Lesson two. Now that they’re extinct, the Jedi are romanticized, deified…”
In that context, I think the line might read better as:
Luke: “Rey, lesson three. Some things are stronger than blood.”