Generally refer to all kinds of wickedness and transgression of the law, but in the languages of the Scriptures "iniquity" also means, the punishment by which sin is atoned for. As for instance, when it is said that Aaron "may bear the iniquity of the holy things" (Ex. 28:38), it means that he was to atone for the impurity which may have adhered to them. In the same way, "sin" means not only an overt act, but also the atonement for sin. The sense here seems to be:
Wo unto them who, in their vanity, are clamoring
for the punishment of others,
And pulling for retribution
As with cart ropes,
Saying, Let him make speed and hasten his work
That we may see it;
And let the counsel of the Holy One of
Israel draw nigh and come
That we may know it.
Comp. 2 Peter 3:3-14: "There shall come, in the last days, scoffers, walking after their own lusts and saying, Where is the promise of his coming? For since the fathers fell asleep, all things continue as they were from the beginning of the creation. ... The Lord is not slack concerning his promise as some men count slackness; but is long suffering to usward, not willing that any should perish but that all should come to repentance. But the day of the Lord will come as a thief in the night."