Why should we never trust an evil man to administer justice? It is because a wicked man is morally confused. His mind is not filled with what is just - but rather with what his own flesh desires. He is not led by the Spirit of God, Who takes the Word of God and instructs us in what is right and true. He is led by the spirit of this world, which, when it does not get what it wants, it kills and steals and decides rules do not apply.
To grasp what this proverb is saying we must once again delve into the whole concept of evil. The philosophies of today do not recognize evil - or call it what it is. They state that man is basically good and if left to himself, without negative influences, would self-evolve into everything that is right and good and perfect. The evil man does not acknowledge God or that God's Word is right and true in all things. Thus he is blind when it comes to true justice.
The word "justice" here also needs to be discussed for a moment or two. This word is "mishpat" in the Hebrew - and it actually means "judgment." The judgment spoken of here is that of God. Israel was expected to uphold true justice. God warned her leaders that they should decide with justice between two brothers in conflict. God declared what is right - and men were to take what is true and right and use it for judgment and the administration of true justice. The place we find this "right" and "truth" upon which justice can be understood and practiced is God's Word. It is written down - and it is absolute truth. All other truths in the world must conform to it - or be found wanting - and be untrue. Oh, how the world hates this kind of talk. "Mollify your statements man," they say with teeth clenched. But the fact is always the same that the Bible IS truth. If you want justice - you will have to judge according to what God has to say on the issue. Nothing else will do - and nothing else ultimately matters. The fact that evil men reject God's Word and choose instead to decide things by what they think, is the very reason they do not understand justice.
The second half of this proverb states the opposite aspect of this truth. Those who seek the LORD (who seek Jehovah God) understand all things. Those who seek the Lord - and do so in truth - seek Him through His revelation of Himself in the Word of God. This is the ONLY place where you get accurate information about God and Who He is. When we seek Him and know Him through what His Word teaches us about Him - then we not only understand justice - but we understand all things. Both times the word "understand" is used it refers to the ability to discern or to perceive what is right. It means being able to distinguish between two things. You see the world - you see the Word - and you can make a viable decision on what God wants in any situation.
Note here that we find that justice is not the only thing you receive when you seek the Lord. The wicked cannot even grasp justice alone - but the man seeking God - gets it all. He understands and can discern all things. There is the glory of knowing and loving the Lord. You don't get just wisdom - or justice - or joy - you get all things. Having Him - you have it all! Paul said in Colossians that in Christ was all the riches of wisdom and understanding. Those who seek Him understand ALL things! Thus the goal of our lives should be to seek and to know Him. We don't study the Bible to become more spiritual - or more wise - or bolder - or anything else. We study and know the Word because when we do - we get everything. God gives it all to us in Christ. Having Him we have everything.
Evil men should not be trusted to know and administer justice. The man who can be trusted to make decisions and judgments for an entire society - is the man who desires to know God with all that is in him. Find that man - and you will find the one who understands all things - not just justice - but the meaning of life itself.