system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] Why did Luke use a green lightsaber rather than a blue one?

From what I understand, a blue lightsaber means that you view the force as a tool to accomplish tasks—that you prefer to use the force on a physical level. A green lightsaber, however, means that you view the force itself as an end goal—that you use it on the spiritual level, and wish to study it purely for the sake of knowledge.

Luke seems more like a blue wielder than green. He’s always been pushy and anxious to use the force to do things, rather than just to study the force. Qui-Gon and Yoda are definitely green wielders, because they are very spiritual with their studies, but Luke only ever learns what he needs to know in order to succeed; he never had much of a thirst for knowledge.

So why did he choose green and not blue?
gpt
Luke didn't know any of that stuff, he was just building a new lightsaber.  The meanings to colors were lost with the Old Republic. Whatever crystal he found to use was apparently green.  He didn't have any higher meaning to it.  

He might have chosen green because of traumatic reactions to blue.  He did have quite a time at Cloud City with a blue lightsaber, he found out his father was alive but evil and had his hand cut off.