In what way was Luke's training "incomplete"?

Question

In Star Wars Episode V: The Empire Strikes Back, Yoda and Obi-Wan both encourage Luke to stay on Dagobah to finish his training. They beg him:

YODA: Luke, you must complete the training.

LUKE: I can’t keep the vision out of my head. They’re my friends. I’ve got to help them.

YODA: You must not go.

He refuses them and leaves for Bespin to save his friends.

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The next time we see Yoda, in Star Wars Episode VI: Return of the Jedi, he tells Luke that he's dying. The conversation continues:

LUKE: But I need your help. I’ve come back to complete the training.

YODA: No more training do you require. Already know you that which you need.

LUKE: Then I am a Jedi.

YODA: Oh! Not yet. One thing remains... Vader. You must confront Vader. Then, only then, a Jedi will you be.

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If the only thing left in Luke's training is to confront Vader, why are Yoda and Obi-Wan so concerned with him leaving to do exactly that?

If he already knows "that which he needs", why wouldn't they simply drop the bomb (Vader=Anakin) and just say "go get him, good luck"?

Was there some additional training that we didn't see? Possibly after Luke returned to Dagobah but before Yoda's death?

Answer 1

See Where did Luke train between ESB and RotJ, there was actually about a year between the two films during which Luke had time to train more. It was during this time that he built his green lightsaber. By the time we see him again in Return of the Jedi, he seems less impulsive, more sure of himself, and stronger in the Force.

More importantly, in Empire Strikes Back Luke learned a couple of valuable lessons. As you mentioned, he learned the truth of Darth Vader's identity, but more importantly he learned that he couldn't solve all of his problems with a lightsaber.

Remember before entering the cave on Dagobah, Yoda told Luke to leave behind his weapons and he refused. And then Yoda told him not to face Vader and he went anyway. Later, in Return of the Jedi it's Yoda, not Luke, who suggests facing Vader (showing that Luke has learned humility and patience). And when the confrontation happens, Luke freely surrenders his weapon, trusting in the Force and the love of a father for his son.

It seems to me that for these reasons, Yoda changed his mind and accepted that Luke was finally ready to fulfill his destiny.

Plus, Leia was Yoda's backup plan. So he had to keep Luke alive until she escaped from Bespin. After that, it didn't matter as much.

Answer 2

He wanted Luke to resist the dark side to be a jedi, and he feels that Luke isn't capable of resisting when Vader or Sideous tempt him(remember, Luke had just shown he wasn't even able to lift a x-wing with the force, meaning that he might be tempted by a chance to learn more easily)

[Luke sees his X-Wing is about to sink into the bog] Luke: Oh, no! We'll never get it out now!

Yoda: So certain, are you? Always with you, what cannot be done. Hear you nothing that I say?

Luke: Master, moving stones around is one thing, but this is... totally different!

Yoda: No! No different! Only different in your mind. You must unlearn what you have learned.

Luke: All right, I'll give it a try.

Yoda: No! Try not. Do... or do not. There is no try. [Luke tries to use the Force to levitate his X-Wing out of the bog, but fails in his attempt.]

Luke: I can't. It's too big.

Yoda: Size matters not. Look at me. Judge me by my size, do you? Hmm? Hmm. And well you should not. For my ally is the Force, and a powerful ally it is. Life creates it, makes it grow. Its energy surrounds us and binds us. Luminous beings are we, not this crude matter. You must feel the Force around you; here, between you, me, the tree, the rock, everywhere, yes. Even between the land and the ship.

Luke: You want the impossible. [sees Yoda use the Force to levitate the X-Wing out of the bog and gets flustered when he does it] I don't... I don't believe it!

Yoda: That is why you fail.

Therefore, Yoda thought that Luke shouldn't go. Yoda probably thought after he (Yoda himself that is) lost to Sidiuos. He probably then made the idea that to become a Jedi, someone needed to resist the dark side, or better yet defeat a sith..

Yoda says: "You must confront Vader. Then, only then, a Jedi will you be."

Therefore, after Luke comes back, Yoda sees he can handle a sith, therefor saying his training is complete.

Props to Darth Vader (the actual account person on this website) for suggesting the Resisting the dark side idea. Before it was all just defeating a sith.

Answer 3

Yoda and Obi-Wan wanted Luke to finish his training, but Luke would not stay since he wanted to go save his friends. The training he had not finished was his Force training, most likely, and controlling his emotions. Yoda thought Luke would fall to the dark side because of his emotions, as Anakin did before him. So, as you can tell, what Yoda was wanting was to teach Luke how to control his emotions. In Return of the Jedi, Luke has learned more about controlling the Force and controlling his emotions; I am certain he has learned to control his emotions, as because Luke fought Vader on Bespin and learnt his father was actually Vader, he seemed to handle his emotions well afterwards, as he hadn't fallen to the Dark side due to them.