The Imrei Noam (authored by Rebbe Meir of Dzikov) further expounds on this, citing the Midrash and the Zohar, on the greatness of the elevation that takes place at this time of Minchah of Erev Shabbos... when the forces of impurity cry over their disconnection from kedushah, and a Yid prepares to experience a ייחוד with the Ribbono shel Olam.
All this transpires on Erev Shabbos at Minchah, and this is what we say in כגוונא at the culmination of Kabbalas Shabbos: שבתא דמעלי צלותא, during the tefillah of Erev Shabbos, all the forces that have tethered themselves to the kedushah of Shabbos and draw vitality from it (like a person who has connected his home to an illegal source of electric power) are cut off. They want to draw chiyus from the Source that animates and gives vitality to the world—but on Erev Shabbos at Minchah, we untether them and cut off their sustenance. This is a great part of the avodah of Minchah of Erev Shabbos.
