Summary

• The introduction of the Sith Rule of Two adds depth to Palpatine and Vader's conversation, suggesting that they both saw themselves as Luke's new master and wanted to utilize his power for their own gain.
• If Luke had joined Vader, it would have put Vader on the Emperor's throne with Luke as his apprentice, potentially leading to a power struggle and the risk of someone dying.
• This scene gains even more depth with the Sith Rule of Two, as Vader's idea of gaining Luke as an asset could have resulted in death, either Luke's or Palpatine's.

The Sith Rule of Two retcons a scene from The Empire Strikes Back in a way that only enhances it even more. It was in Star Wars: Episode I - The Phantom Menace that the Sith Rule of Two was first introduced by Yoda following the death of Qui-Gon Jinn at Darth Maul's hands. He insisted there could only ever be one master and one apprentice of the Sith, "no more, no less," an idea that has since earned its origin with Sith Lord Darth Bane.
Your browser does not support the video tag. In The Empire Strikes Back, however, there's a scene that has since been retconned by the introduction of the Sith Rule of Two. When Emperor Palpatine and Darth Vader discuss the disturbance in the Force that's been caused by Luke Skywalker, Vader suggests that they make Luke an ally rather than simply seeking to destroy him, an idea Palpatine agrees with. This exchange seems to be contradicted completely by the Rule of Two, in which no Sith would ever dare take on a third and threaten the master-apprentice relationship. But taking another look at their exchange with the rule in mind gives it a new and interesting spin.
The Rule of Two guarantees the continuous growth of the Sith by nurturing power and cunning with each new generation.

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