The word adikia is used multiple times in the New Testament, and is rendered by different words like unrighteousness or iniquity. In order to not burden ourselves, we will take it in several installments.
Jesus claimed to have “no unrighteousness” in Him, because He was seeking the glory of the one who sent Him (John. 7:18). We see here that the heart of unrighteousness is seeking glory for self in a selfish way. At the same time, a person can be surrounded by this kind of self-seeking, this unrighteousness, and yet not participate in it the same way. “And I say unto you, Make to yourselves friends of the mammon of unrighteousness; that, when ye fail, they may receive you into everlasting habitations” (Luke 16:9). We are told to use the crooked unrighteous instruments of the world, and straighten them out for God’s purposes.
Not surprisingly, unrighteousness is an important theme in the book of Romans. It is used twice in Romans 1:18. God’s wrath is revealed from heaven against every form of ungodliness and unrighteousness, and this unrighteousness of men is revealed even further in that they suppress the truth in unrighteousness. Unrighteousness does not just love the false, but also hates what is true.
Later in the chapter (v. 29), Paul gives us the genus (unrighteousness), and then lists some of the species. The list that follows is extensive — fornication, wickedness, covetousness, maliciousness, and on, for three verses. Unrighteousness wields authority, and commands sinners to do things. Man is created such that he must be obedient — he either obeys the truth, or he obeys unrighteousness. One or the other. In the Pauline set up, the opposite of true is not false, but rather unrighteous. He also does this in another letter. Unrighteousness is deceptive, and that is the way Satan works (2 Thess. 2:10). The contrast (again) is between unrighteousness on the one hand, and truth on the other. Those who did not believe the truth are those who had pleasure in unrighteousness (2 Thess. 2:12). Truth is not merely propositional; truth is moral.
Back in Romans, some had argued that our unrighteousness sets off God’s righteousness in some kind of complimentary relief (3:5). That’s true enough, but it does not provide a sufficient reason why the righteous God would withhold judgment. The fact that God sovereignly disposes of both Jacob and Esau does not mean that He is unrighteous (9:14).
Christians are told not to deliver their members, their bodies, over to sin as instruments of unrighteousness (6:13). This means that Christians can do this kind of unrighteousness, but their new identity in Christ makes it a profound incongruity. Paul grabs that incongruity in order to shake them.
But God has had mercy on the unrighteous (Heb. 8:12). He cleanses us from all unrighteousness (1 Jn. 1:9). All unrighteousness is sin (1 Jn. 5:17), and sin is lawlessness. Apart from repentance, those given over to unrighteousness will reap what they have sown. They will receive the reward of unrighteousness, the wages of sin, which is death (2 Pet. 2:13). They are like Balaam, who loved the wages of unrighteousness (2 Pet. 2:15).