Charles H. Spurgeon on Psalms 130:3

Iniquities. The literal meaning of the word "iniquity" is "a thing which is not equal", or "not fair." Whatever breaks a command of God is "not equal." It does not match with what man is, nor with what God is. It does not keep the high level of the law. It is altogether out of proportion to all that God has done. It destroys the harmony of creation. It does not rise even to the height of conscience. Still more, it mars and makes a flaw in the divine government. Therefore sin is an unequal thing, fitting nothing, disarranging everything. And it is not fair. It is not fair to that God upon whose empire it is a trespass. It is not fair to your fellow creatures, to whom it may be a very great injury. It is not fair to yourself, for your happiness lies in obedience. Therefore we call sin "iniquity." Or, as the Prayer Book Version expresses the same idea, "a thing amiss", missing its proper mark. "If thou shouldest be extreme to mark what is done amiss." —James Vaughan.