Matthew Poole and continuators on Jeremiah 2:22

22 For though thou wash thee with nitre, and take thee much sope s, yet thine iniquity is marked before me, saith the Lord GOD.

The meaning seems to be either thy filthiness is so foul, that it leaves a brand behind it, that cannot be hid or washed out, but will abide; see Ier. 17.1. Or, according to another acceptation of the word, it is laid up with God, see the like Deut. 32.34. and Hos. 13.12. purge thee, wash thee, do what thou wilt, thou canst by no means conceal thy wickedness from me, Iob 9.20. they that would see greater variety of interpretations, let them consult the Synopsis.

Though interpreters do greatly vary in describing what is particularly meant here by Nitre and Sope, and would be superfluous to mention here, yet all agree they are some materials that Artists make use of for the cleansing away spots, from the skin, cloaths, or other things: and the sense is plain, that the blot of his People is by no art to be taken out, it cannot be covered by excuses, though thou wouldst dissemble thy Idolatries, thou canst not deceive me: nor explated by sacrifices, it is beyond the Power of all superstitious, or religious washings to cleanse away, which may be understood by these natural and artificial wayes of cleansing.

Marginal references: Job 9.30.; Job 14.17.