Because he has a light saber? If you watch the movies, Jedis are always losing their light sabers. It’s something of a galactic epidemic. And with that, they are landing in the hands of all kinds of folks — General Grevous, for example, had a whole collection of them, and he was no Jedi. So, just having a glowing stick sword thing isn’t enough to be a Jedi.
Because the Force is strong in him? Well, no. The Force is in everyone and everything, and not everyone or everything is a Jedi. The Republic was ready to skip on ol’ Anakin when he was found, because he was “too old” — even knowing that his midi-chlorians were the highest ever recorded. There’s no benchmark for midi-chlorians levels, or the Force in someone. No Kelly Blue Book.
Because he graduated from the Jedi Academy? Well, no. He wasn’t identified at a young age, wasn’t brought into the bosom of the Jedi community, wasn’t raised and trained as one. He didn’t take part in the formal Jedi culture that had existed for the thousands of years of the Republic. He just picked up a light saber and went at it.
Because a Jedi trained him? Well, no. Yes, Yoda did train him, but no, that’s not enough. The Jedi Council confers the title of Jedi Knight — and if you recall, that frustrated the hell out of Anakin, as he felt he was ready / worthy of the title, and they did not. Just studying under a Jedi Knight isn’t enough.
I know what you’re thinking – by Luke’s time, there was no Jedi Council. Thus, there could be no new Jedi Knights.
Yep. I totally agree. Luke Skywalker — poser. He’s the Bill S. Preston Esq. of the future. He should not be calling himself a Jedi Knight — pick a new name for whatever it is that he thinks he is.