Jeremiah 2:22

For though thou wash thee with nitre
The word (rtn) , "nitre", is only used in this place and in ( Proverbs 25:20 ) and it is hard to say what it is. Kimchi and Ben Melech observe, that some say it is what is called "alum"; and others that it is a dust with which they wash the head, and cleanse everything; and so Jarchi says it is a kind of earth used in cleaning garments; and "nitre" is mentioned by the Misnic doctors ^F19 among those things which are used for the washing of garments, and taking spots out of them; though about what it is they are not agreed; and it seems the nitre of the ancients is unknown to us {t}; and saltpetre is put in the room of it; and some render the word here "saltpetre"; and Pliny ^F21 observes, that nitre does not much differ from salt, and ascribes to it a virtue of eating out filth, and removing it; so Aristotle ^F23 reports of the lake Ascania; that its water is of such a nitrous quality, that garments, being put into it, need no other washing. Nitre has its name from (rtn) , "to loose", because it looses the filth, and cleanses from it: and take thee much soap.
The Septuagint render it, "herb"; and the Vulgate Latin version, "the herb borith"; which is the Hebrew word here used; and about the sense of which there is some difficulty. Kimchi and Ben Melech say some take it to be the same with what is called "soap"; so Jarchi; and others, that it is an herb with which they wash, the same that is called fullers' herb; but whether it is soap, or fullers' herb, or fullers' earth, as others, it is certain it is something fullers used in cleaning garments, as appear from ( Malachi 3:2 ) , where the same word is used, and fullers made mention of as using what is signified by it. It has its name from (hrb) , which signifies to "cleanse" and "purify". The sense is, let this backsliding and degenerate people take what methods they will to cleanse themselves from their sins, as by their ceremonial ablutions and sacrifices, which was the usual method they had recourse to, to purify themselves, and in which they rested: yet thine iniquity is marked before me, saith the Lord God;
or, "will retain its spots" ^F24 these remain; the filth is not washed away; the iniquity is not hid and covered; it appears very plain and manifest; yea, shines like gold;
or, "is gilded" ^F25; as the word used signifies. It is of too deep a die to be removed by such external things; nothing but the blood of Christ can cleanse from sin, take away its filth, removes its guilt, and cover it out of the sight of God, so that it can be seen no more. The Targum is,

``for if you think to be cleansed from your sins, as they cleanse with nitre, or make white with "borith", or soap; lo, as the mark of a spot which is not clean, so are your sins multiplied before me, saith the Lord God.''