Tanya for the 16th and 17th of Menachem Av, ט׳׳ז-י׳׳ז מנחם אב

The Alter Rebbe now goes on to explain that the letters of speech are composed of “matter” and “form” the “body” and “soul” (or: the external and internal aspects) of the letters. While the “form” of the letters does indeed derive from chochmah, the “matter” of the letters of speech merely derives from the heart.