The way I learned it was that sin = hamartia, “missing the mark.” Wrong but you don’t even it’s wrong, like marrying your mother.
Iniquity is wrong that you know is wrong but do it anyway.
I don’t think that I can agree with this…. first of all, hamartia has a few definitions but most commonly, it’s defined as a ‘flaw in one’s character’. Somehow I don’t think this is synonymous with sin which is a ‘willful or deliberate violation of a Godly principle or to put it another way, direct transgression that runs counter to how God wants us to live our lives’. I think that sin can be considered to be the direct action while iniquity was the depraved thinking that lead up to that action. Let’s take an obvious example…. The act of murder is an obvious and direct violation against God’s law for how we are to live. Jealousy and covetousness might have been the iniquity that caused on to commit that murder. Hence…. Sin is the fruit but iniquity is the root. Titus 2:14 says this….. “Who gave himself for us, that he might redeem us from all iniquity, and purify unto himself a peculiar people, zealous of good works.” In other words, we can be thankful that God not only can cleanse us from our sins, He can take away the depraved thinking that lead us to commit those sins….. a purifying of the mind. This is also the thought in Romans 12:2 “And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God.”