Charles Ellicott Commentary Jeremiah 16:18

"And first I will recompense their iniquity and their sin double, because they have polluted my land with the carcasses of their detestable things, and have filled mine inheritance with their abominations." — Jeremiah 16:18 (ASV)

I will recompense their iniquity and their sin double. —A restitution, or fine, to double the amount of the wrong done was almost the normal standard of punishment under the Law of Moses (Exodus 22:4; Exodus 22:7). The words threaten accordingly a full punishment according to the utmost rigor. In Isaiah 40:2 the same thought is presented in its brighter aspect. Israel has received double for all her sins, and therefore, having paid, as it were, the uttermost farthing (Matthew 5:26), she may now hope for mercy.

The carcasses ... —The word may be used in contempt of the lifeless form of the dumb idols which the people worshipped, touching which caused pollution, as by contact with a corpse (Numbers 19:11); but it more probably points to the dead bodies of the victims that had been sacrificed to them. The phrase also occurs in a similar context in Leviticus 26:30. It would appear from Isaiah 65:4 that these often included animals which by the Law were unclean: swine’s flesh and broth of abominable things.