This is the same as we said above (Opening 27) regarding the Residue. It is a category in the sense that it includes the entire array of all the details into which it will divide, but it is called a single material or substance (i.e. the Residue constitutes the overall category of Tzimztum and is also the “substance” that includes the entire creation). It is a single substance in the sense that it constitutes the totality of all the individual entities that must divide into their various divisions, each one by itself, according to their appropriate form.