Obi-Wan’s lies to Luke Skywalker throughout the original Star Wars trilogy are revealed in Return of the Jedi - but deleted Yoda dialogue would have redeemed Kenobi. Darth Vader’s revelation that he is Anakin Skywalker in The Empire Strikes Back is perhaps the greatest plot twist in the Star Wars franchise, though it also reveals that Obi-Wan (Alec Guinness) and Yoda (Frank Oz) had been lying to Luke (Mark Hamill) about his father. Yoda’s lines in the scrapped Return of the Jedi footage soften the blow quite a bit, however, adding nuance to both of the Jedi's decades-long deception.
In A New Hope, Luke is told by Obi-Wan that Anakin Skywalker was a Jedi hero who Darth Vader betrayed and killed. The original Star Wars trilogy wasn’t fully mapped out at this point, so while George Lucas had considered making Darth Vader secretly Luke’s father, he wouldn’t truly canonize it until reworking Leigh Brackett’s story treatment for Empire. At the behest of Richard Marquand, who had consulted a psychologist on the matter, Lucas allowed Return of the Jedi to include an additional scene on Dagobah, in which Yoda and Obi-Wan reveal the whole truth of their plan to defeat the Sith to Luke.
Unused footage of Yoda’s death scene in Return of the Jedi would have added an additional layer to his and Obi-Wan’s lies. Yoda admits to Luke, “Obi-Wan would have told you long ago, had I let him,” indicating that neither Jedi wanted to keep Luke in the dark but did because they believed it was the best course of action to do so defeat Darth Vader and The Emperor. With this added context, Obi-Wan and Yoda’s deceit, while still morally questionable (considering that they were training Luke to kill his father), seems far more reluctant and tragic on both of their parts while speaking to the continued failings of the old Jedi Order.
How Yoda's Cut ROTJ Dialogue Further Explains Obi-Wan's Lies
Yoda, Obi-Wan, and Bail Organa (Jimmy Smits) create their long-term plan to defeat the Sith at the end of Star Wars: Episode III – Revenge of the Sith. Once the time was right, one or both of Anakin’s children would be trained as a Jedi to kill Vader and the Emperor, freeing the galaxy and allowing the Jedi to return. Unfortunately, the plan also involved keeping Luke and Leia in the dark as far as their father’s true identity, something that Yoda’s deleted dialogue indicates was not a decision made lightly.
Obi-Wan would have wanted Luke to know the truth from the beginning, but he and Yoda couldn’t take any chances with the galaxy's fate in jeopardy. Unfortunately, had everything gone according to plan, Luke would have learned of his father’s true identity after killing him, which would likely be a traumatizing revelation in that context. While Obi-Wan and Yoda had the best intentions in mind and wished that Luke could know the truth, they ultimately perpetuated issues with their generation of Jedi instead.
The old Jedi Order had an unfortunate tendency to make morally questionable decisions for the greater good. This included recruiting potential Jedi as infants and functioning as a paramilitary force for Republic politicians. While hiding the truth from Luke and nearly pushing him to unknowingly commit patricide was, understandably, frustrating to Luke once he learned the truth, Return of the Jedi’s deleted dialogue shows that Obi-Wan and Yoda were ultimately not happy with their actions, either.