RoccondilRinon said:

Could work.

Yoda said:

A Jedi uses the Force for knowledge and defence. Never for attack.

And elsewhere, Jedis activate their lightsabres to show that they are not defenceless, and to try to warn off an attack; in ANH:R, Adywan made the significant change of having Vader waiting for Obi-Wan with his sabre turned off, and Obi-Wan activating his first. Of course, unless Yoda or Obi-Wan specifically told him of this, Luke wouldn't know it, but Vader is definitely right in calling him unwise.

Exactly why did Ady make this change?