Musar for Isaiah 4:3

The Torah tells of Abraham giving gifts to the sons of his concubines (Genesis 25,6), and Sanhedrin 91a describes these "gifts" as שם טומאה, i.e. Abraham did not want them to refer to Satanic forces by the name of G–d (Torah Temimah on that verse). The reason that the word פלגשם in that verse is spelled defectively, without the letter י to indicate the plural ending, is to allude to the name i.e. שם of the קליפה. Read פלג-שם, the name divided, and you have a hint of the dichotomy of forces, which is what סטרא אחרא and טומאה is all about. In the future this process will be reversed and טומאה will vanish.