John Wesley on Jeremiah 2:22

Nitre - Though interpreters do greatly vary in describing what is particularly meant here by Nitre and Soap, and would be superfluous to mention here; yet all agree, they are some materials that artists make use of for cleansing away spots from the skin. The blot of this people is by no art to be taken out; nor expiated by sacrifices; it is beyond the power of all natural and artificial ways of cleansing. Marked - Thy filthiness is so foul that it leaves a brand behind which cannot be hid or washed out, but will abide, Jer 17:1.