Jeremiah 2:22 - Joseph Benson’s Commentary on the Old and New Testaments

For though thou wash thee with nitre, &c. Though thou shouldest use ever so many methods of washing away thy sins, such as the rites of expiation prescribed by the law, or practised by idolaters; though thou shouldest insist ever so much upon thy own innocence and righteousness, yet the marks or stains of thy sins will always appear in the sight of God, till they are done away by his pardoning mercy, exercised toward thee in consequence of thy repentance and reformation. “The nitre here mentioned is not what we call nitre, or salt-petre, but a native salt of a different kind, distinguished among naturalists by the name of natrum, or the nitre of the ancients. It is found in abundance in Egypt, and in many parts of Asia, where it is called soap-earth, because it is dissolved in water, and used like soap in washing.” Blaney.