There is a lot going on here, too much to describe everything in detail. However, the original Greek doesn’t necessarily mean as it is translated:
First, the word translated as “for” (Εἰς, is) isn’t the word usually translated as “for” in the sense of describing a purpose. It is almost always translated as “into”. It can mean “for” in describing a purpose, but Jesus usually uses another, less ambiguous word to do that.
Next, the Greek word translated as "judgment" (κρίμα, krima) is not the word we usually see translated as "judgment" in the NT (krisis). Neither word captures our idea of judgment exactly. Krisis means judgment in the sense of choosing, deciding, and separating. Krima is a pronouncement of judgment, a decree or a sentence, the announcement of a decision made by a leader.
"The world" is better understood as "society." The word is kosmos (κόσμον), which refers to the order of society. The word translated as “this” means “the nearer”, so the reference is specifically to Jewish society,
There is a lot more here, but you can look at the actual meaning of the Greek word inthis more detailed article.
One more literal translation of this verse could be:
In regard to a decree, I myself have shown up in this here society so that those who are not watching might watch and those [now] watching might become lacking in a vision of the future.