If you end your training now, if you choose the quick and easy path, as Vader did, you will become an agent of evil.
11 seconds sound clip from the Star Wars: Episode V - The Empire Strikes Back movie soundboard.
You can hear this line at 01:24:13 in the Blu-ray version of the movie.
Quote context
[...]
- Luke, I don't want to lose you to the emperor the way I lost Vader.
- Stopped they must be. On this all depends.
- Only a fully trained Jedi knight, with the Force as his ally, will conquer Vader and his emperor.
- If you honor what they fight for... yes.
- If you choose to face Vader, you will do it alone. I cannot interfere.
[...]