The Line, on the other hand, is the root of the soul, and it proceeds through the power of His unity to rule over all parts of the Residue, ultimately proving that everything that appears to be the opposite of truth through the power of the concealment actually turns around to show the real truth and reveal His supreme unity. This will come about in actuality when the world comes to complete perfection, when all evil will already have reverted to good, this being the function of the Line. The Residue will then no longer be something that repels the Supreme Perfection. On the contrary, what will show the power of His true perfection is precisely the repair of all the apparent defects seen in the world through the revelation of His unity.
The Kav as the Root of the Soul's Mission
Kalach Pitchei Chokhmah 41:8