The carcasses of their detestable - things - Either meaning the idols themselves, which were only carcasses without life; or the sacrifices which were made to them.
First - Before the return from exile.
I will recompense their iniquity double - The ordinary rule of the Law (Isaiah 40:2 note). Sin is twofold; there is the leaving of God‘s will undone, and the actual wrongdoing. And every punishment is twofold: first, there is the loss of the blessing which would have followed upon obedience, and secondly, the presence of actual misery.
Because they have defiled - Rather, “because they have profaned My land with the carcases of their detestable things” (their lifeless and hateful idols, the very touch of which pollutes like that of a corpse, Numbers 19:11); “and hare filled My inheritance with their abominations.”