We are all as an unclean thing... — Better, as he who is unclean, scil., like the leper of Leviticus 13:45.
Filthy rags point to that which to the Israelite was the other extremest form of ceremonial uncleanness, as in Ezekiel 36:17.
Have taken us away — scil., afar off from the light and favour of Jehovah.