unclean thing - legally unclean, as a leper. True of Israel, everywhere now cut off by unbelief and by God’s judgments from the congregation of the saints.
righteousness - plural, “uncleanness” extended to every particular act of theirs, even to their prayers and praises. True of the best doings of the unregenerate (Phi 3:6-8; Tit 1:15; Heb 11:6).
filthy rags - literally, a “menstruous rag” (Lev 15:33; Lev 20:18; Lam 1:17).