I think the parallel that is drawn between runners and learners in #5 is actually very interesting in terms of what Confucius is getting at. To learn effectively, this phrase seems to be saying, we have to train ourselves and work at it with perseverance and dedication. Only by learning in this way will we gain the full benefits of learning.
This seems to suggest that hard work can actually give pleasure. This idea may at first sound strange, but consider the parallel with exercise, such as running. The runners I know work very hard at their sport, but their running gives them enormous physical and mental satisfaction. They keep challenging themselves to push even harder and farther, and each goal accomplished only leads to another, harder goal. Confucius seems to have felt that the same kind of pleasure can be derived from the hard work of learning and becoming educated, and I think he's right. (That's why he's Confucius!)
To me, this statement means that true learning requires extensive dedication that does not allow the student to slow down or kick back. Applying oneself indicates a deep dedication without ceasing, and perserverance indicates working hard even when it hurts: learning—as said earlier—is not easy, but I would assume that Confucius felt this was required of earnest students and that one should expect no less of himself if he is truly dedicated to learning.
I think #5 right too.
Perseverance and Dedication (at 3 different levels) - the first point of Confucius in Analects.
I am through with this project and appreciate all the explanations that were sent.