Maybe figuring out there is no Lesson 3 is the lesson?
I just always assumed things got out of hand between Luke and Rey before they could get to a third lesson. This deleted scene certainly sounds like a lesson since Luke set it up to reach Rey… a lesson. About the Jedi. I don’t know.
Jedit:
Maybe the deleted scene is more like a test. To see if Rey is worthy of being a Jedi.