Quick answer
Some things are not visible from certain positions. The verse says justice is one of them, and that seeking God is what clears the view.
Read both lines
The word is מִשְׁפָּט, justice, the term carrying this book's concern for whoever cannot enforce their own case, and the claim is about comprehension rather than compliance. Evil men do not understand it. That is more unsettling than saying they ignore it, because a man who cannot see the thing will not experience himself as refusing it.
The second line's "understand all" is sweeping, and the parallel keeps it in bounds: set against the first line, it means those who seek the LORD understand all of this, all of what justice requires, rather than becoming omniscient. Chapter 21 said the wicked refuse to do justice; this says they cannot see it, and the two together explain why arguing with them about it so rarely works.
Related: Proverbs 21:7 · Proverbs 21:15 · Proverbs 29:7 · Proverbs 13:23
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.