All this is found above in the Line and the Residue. Before the Line could be joined with the Residue in a genuine connection that would cause everything to go in one direction, the Residue had to be allowed to do everything in its power – i.e. to actually bring forth any evil that could develop out of it, so that afterwards it will be pure of this evil, as will be discussed below. The Line will then join with it in a complete bond, as when it first entered into it, and just as it shone before the breaking of the vessels, so it will shine afterwards with their rectification.
Kabbalistic Insight of Residue
Kalach Pitchei Chokhmah 41:12