Now, sin is the transgression of the law; and I would venture to say that it is reasonable to say that sin is iniquity.
Therefore, iniquity is the transgression of the law (while iniquity, by definition, goes deeper than that).
Now, consider.
Mat 7:23, And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.
Mat 25:41, Then shall he say also unto them on the left hand, Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels:
Mat 13:41, The Son of man shall send forth his angels, and they shall gather out of his kingdom all things that offend, and them which do iniquity;
Mat 13:42, And shall cast them into a furnace of fire: there shall be wailing and gnashing of teeth.
Jesus came to save His people from their sins (Matthew 1:21) and to redeem us from all iniquity (Titus 2:14).
Those who have not been redeemed from sin (see Romans 6:22) are still cursed by the law because they fail to obey it; and therefore it condemns them.
Those who are forgiven and justified through Jesus' blood are counted as unshakably righteous even if they blow it (Romans 4:5).
The exhortation from that point is to go and live like their new identity (1 John 3:7, Romans 5:19, Matthew 5:6).
So, there is a practical outworking to imputed righteousness; wherein righteousness is also imparted to the one to whom it has been imputed (again, 1 John 3:7, Romans 5:19, Matthew 5:6).